OLED lighting device with short tolerant structure

ABSTRACT

An OLED panel having a plurality of OLED circuit elements is provided. Each OLED circuit element may include a fuse or other component that can be ablated or otherwise opened to render the component essentially non-conductive. Each OLED circuit element may comprise a pixel that may include a first electrode, a second electrode, and an organic electroluminescent (EL) material disposed between the first and the second electrodes. Each of the OLED circuit elements may not be electrically connected in series with any other of the OLED circuit elements.

CROSS-REFERENCES TO RELATED APPLICATIONS

This application is a continuation-in-part of U.S. application Ser. No.13/349,295, filed Jan. 12, 2012, which claims benefit under 35 U.S.C.§119(e) of U.S. provisional patent application No. 61/431,985, filed onJan. 12, 2011, each of which is incorporated herein by reference for allpurposes and in their entireties.

The claimed invention was made by, on behalf of, and/or in connectionwith one or more of the following parties to a joint universitycorporation research agreement: Regents of the University of Michigan,Princeton University, The University of Southern California, and theUniversal Display Corporation. The agreement was in effect on and beforethe date the claimed invention was made, and the claimed invention wasmade as a result of activities undertaken within the scope of theagreement.

FIELD OF THE INVENTION

The present invention relates to devices having organic light emittingdevices, and more particularly to devices having organic light emittingdevices that include a short tolerant structure.

BACKGROUND

Opto-electronic devices that make use of organic materials are becomingincreasingly desirable for a number of reasons. Many of the materialsused to make such devices are relatively inexpensive, so organicopto-electronic devices have the potential for cost advantages overinorganic devices. In addition, the inherent properties of organicmaterials, such as their flexibility, may make them well suited forparticular applications such as fabrication on a flexible substrate.Examples of organic opto-electronic devices include organic lightemitting devices (OLEDs), organic phototransistors, organic photovoltaiccells, and organic photodetectors. For OLEDs, the organic materials mayhave performance advantages over conventional materials. For example,the wavelength at which an organic emissive layer emits light maygenerally be readily tuned with appropriate dopants.

OLEDs make use of thin organic films that emit light when voltage isapplied across the device. OLEDs are becoming an increasinglyinteresting technology for use in applications such as flat paneldisplays, illumination, and backlighting. Several OLED materials andconfigurations are described in U.S. Pat. Nos. 5,844,363, 6,303,238, and5,707,745, which are incorporated herein by reference in their entirety.

One application for phosphorescent emissive molecules is a full colordisplay. Industry standards for such a display call for pixels adaptedto emit particular colors, referred to as “saturated” colors. Inparticular, these standards call for saturated red, green, and bluepixels. Color may be measured using CIE coordinates, which are wellknown to the art.

One example of a green emissive molecule is tris (2-phenylpyridine)iridium, denoted Ir(ppy)3, which has the structure of Formula I:

In this, and later figures herein, we depict the dative bond fromnitrogen to metal (here, Ir) as a straight line.

As used herein, the term “organic” includes polymeric materials as wellas small molecule organic materials that may be used to fabricateorganic opto-electronic devices. “Small molecule” refers to any organicmaterial that is not a polymer, and “small molecules” may actually bequite large. Small molecules may include repeat units in somecircumstances. For example, using a long chain alkyl group as asubstituent does not remove a molecule from the “small molecule” class.Small molecules may also be incorporated into polymers, for example as apendent group on a polymer backbone or as a part of the backbone. Smallmolecules may also serve as the core moiety of a dendrimer, whichconsists of a series of chemical shells built on the core moiety. Thecore moiety of a dendrimer may be a fluorescent or phosphorescent smallmolecule emitter. A dendrimer may be a “small molecule,” and it isbelieved that all dendrimers currently used in the field of OLEDs aresmall molecules.

As used herein, “top” means furthest away from the substrate, while“bottom” means closest to the substrate. Where a first layer isdescribed as “disposed over” a second layer, the first layer is disposedfurther away from substrate. There may be other layers between the firstand second layer, unless it is specified that the first layer is “incontact with” the second layer. For example, a cathode may be describedas “disposed over” an anode, even though there are various organiclayers in between.

As used herein, “solution processible” means capable of being dissolved,dispersed, or transported in and/or deposited from a liquid medium,either in solution or suspension form.

A ligand may be referred to as “photoactive” when it is believed thatthe ligand directly contributes to the photoactive properties of anemissive material. A ligand may be referred to as “ancillary” when it isbelieved that the ligand does not contribute to the photoactiveproperties of an emissive material, although an ancillary ligand mayalter the properties of a photoactive ligand.

As used herein, and as would be generally understood by one skilled inthe art, a first “Highest Occupied Molecular Orbital” (HOMO) or “LowestUnoccupied Molecular Orbital” (LUMO) energy level is “greater than” or“higher than” a second HOMO or LUMO energy level if the first energylevel is closer to the vacuum energy level. Since ionization potentials(IP) are measured as a negative energy relative to a vacuum level, ahigher HOMO energy level corresponds to an IP having a smaller absolutevalue (an IP that is less negative). Similarly, a higher LUMO energylevel corresponds to an electron affinity (EA) having a smaller absolutevalue (an EA that is less negative). On a conventional energy leveldiagram, with the vacuum level at the top, the LUMO energy level of amaterial is higher than the HOMO energy level of the same material. A“higher” HOMO or LUMO energy level appears closer to the top of such adiagram than a “lower” HOMO or LUMO energy level.

As used herein, and as would be generally understood by one skilled inthe art, a first work function is “greater than” or “higher than” asecond work function if the first work function has a higher absolutevalue. Because work functions are generally measured as negative numbersrelative to vacuum level, this means that a “higher” work function ismore negative. On a conventional energy level diagram, with the vacuumlevel at the top, a “higher” work function is illustrated as furtheraway from the vacuum level in the downward direction. Thus, thedefinitions of HOMO and LUMO energy levels follow a different conventionthan work functions.

More details on OLEDs, and the definitions described above, can be foundin U.S. Pat. No. 7,279,704, which is incorporated herein by reference inits entirety.

SUMMARY OF THE INVENTION

A first device that may include a short tolerant structure, and methodsfor fabricating embodiments of the first device, are provided. A firstdevice may include a substrate and a plurality of OLED circuit elementsdisposed on the substrate. Each of the OLED circuit elements may includeone, and only one, pixel. Each OLED circuit element may include a fusethat is adapted to open an electrical connection in response to anelectrical short in the pixel. In some embodiments, the OLED circuitelements may include various other components and circuitry in additionto a fuse and the one pixel. Each pixel may include a first electrode, asecond electrode, and an organic electroluminescent (EL) materialdisposed between the first and the second electrodes. Each of the OLEDcircuit elements may not be electrically connected in series with anyother of the OLED circuit elements. In some embodiments, each pixel ofthe OLED circuit elements may include a top or bottom emission OLED, astacked organic light emitting device (SOLED), a transparent organiclight emitting device (TOLED) or any other variation/combination of OLEDdevices. OLEDs may include OLEDs of different colors, for example foruse in color tunable panels, and each may be a flexible OLED.

In some embodiments, a method of fabricating an OLED panel includesobtaining an OLED panel having a plurality of pixels, each pixel beingelectrically connected to a fuse that limits current to the pixel,selecting a plurality of fuses in the OLED panel, and applying energy toeach fuse of the selected plurality of fuses to cause the fuse to beopened. Each fuse may occupy an area of the panel that is not more than10% of the area of the panel occupied by the pixel to which the fuselimits current. Applying energy to the fuses may include directing alaser, such as a UV or IR laser, at the fuse to ablate the fuse. In someembodiments, fuses may be selected based upon one or more stripes ofpixels of a particular color, such as to achieve a desired color in aregion of the panel.

In some embodiments, obtaining the initial OLED panel may includefabricating the panel, for example by obtaining a substrate having afirst electrode, depositing organic emissive material over the firstelectrode, depositing a plurality of physically segmented secondelectrodes over the organic emissive material, depositing insulatingmaterial over the physically segmented second electrodes, wherein aportion of each of the second electrodes remains exposed through theinsulating material, and depositing an unpatterned blanket layer of aconductive material such that the blanket layer of conductive materialelectrically connects to the portion of each of the second electrodesthat remains exposed through the insulating material, to form theplurality of pixels, each pixel being electrically connected to the fusethat limits current to the pixel.

In some embodiments, a method of fabricating a device may includeobtaining a fabricated emissive panel having a plurality of OLEDs, eachof the plurality of OLEDs being electrically connected to a power sourceand having an individual emissive area, selecting a group of theplurality of OLEDs, and, for each OLED of the selected group of theplurality of OLEDs, applying energy to a component of the OLED to causethe component of the OLED to be essentially non-conductive.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 shows an organic light emitting device.

FIG. 2 shows an inverted organic light emitting device that does nothave a separate electron transport layer.

FIGS. 3(a)-(c) show various views of a basic representation of an OLEDboth in normal operation and when a fault occurs in accordance with someembodiments. FIG. 3(a) shows a cross-sectional view of an exemplaryOLED. FIG. 3(b) shows a top view of the exemplary OLED in normaloperation. FIG. 3(c) shows a top view of the exemplary OLED when a faultoccurs.

FIGS. 4(a) and (b) show a top view and a cross-section, respectively, ofan exemplary OLED comprising segmented bus lines before a fault occursin accordance with some embodiments. FIGS. 4(c) and (d) show a top viewand a cross-section, respectively, of the exemplary OLED comprisingsegmented bus lines after a fault occurs in accordance with someembodiments.

FIGS. 5(a) and (b) show a top view and a cross-section, respectively, ofan exemplary OLED before a fault occurs in accordance with someembodiments. FIGS. 5(c) and (d) show a top view and a cross-section,respectively, of the exemplary OLED after a fault occurs in accordancewith some embodiments.

FIG. 6(a) shows a cross-sectional view of an exemplary OLED before afault occurs in accordance with some embodiments. FIG. 6(b) shows across-sectional view of the exemplary OLED after a fault occurs inaccordance with some embodiments.

FIGS. 7(a) and 7(b) show an exemplary OLED before and after a shortfault occurs, respectively, in accordance with some embodiments.

FIG. 8 shows an exemplary OLED panel layout in accordance someembodiments.

FIGS. 9(a)-(d) comprise photographs of experimental results for theimplementation of an exemplary embodiment.

FIG. 10 shows experimental results of an exemplary OLED panel thatcomprises shorted pixels in accordance with some embodiments.

FIG. 11 shows microscopic images of the experimental results from theexemplary OLED panel shown in FIG. 10 having shorted pixels inaccordance with some embodiments.

FIGS. 12(a) and (b) show a top view and a cross-section, respectively,of an exemplary OLED before a fault occurs in accordance with someembodiments. FIGS. 12(c) and (d) show a top view and a cross-section,respectively, of the exemplary OLED after a fault occurs in accordancewith some embodiments.

FIGS. 13(a) and (b) are illustrations of single fuse and multi-fuseexperimental configurations, respectively, in accordance with someembodiments.

FIG. 14 is a graph of current vs. voltage for exemplary fuse designscomprising ITO.

FIG. 15 is a microscopic view of a burnt fuse in accordance with someembodiments.

FIG. 16 is a graph of current vs. voltage for an exemplary fuse designin accordance with some embodiments.

FIG. 17 is a graph of current vs. voltage for exemplary single fuse andmulti-fuse designs in accordance with some embodiments.

FIG. 18 is a graph of current vs. voltage for exemplary fuse designscomprising Al.

FIG. 19 is a microscopic view of a burnt fuse between two contact padsin accordance with some embodiments.

FIG. 20 is a graph of current vs. voltage for exemplary fuses havingdifferent thicknesses in accordance with some embodiments.

FIG. 21 is a graphical illustration of the different currents of anOLED, including exemplary values for melting currents I_(m) of a fuse inaccordance with some embodiments.

FIG. 22 shows an example OLED panel in accordance with some embodiments.

FIG. 23 shows an example OLED panel in accordance with some embodiments.

DETAILED DESCRIPTION

Generally, an OLED comprises at least one organic layer disposed betweenand electrically connected to an anode and a cathode. When a current isapplied, the anode injects holes and the cathode injects electrons intothe organic layer(s). The injected holes and electrons each migratetoward the oppositely charged electrode. When an electron and holelocalize on the same molecule, an “exciton,” which is a localizedelectron-hole pair having an excited energy state, is formed. Light isemitted when the exciton relaxes via a photoemissive mechanism. In somecases, the exciton may be localized on an excimer or an exciplex.Non-radiative mechanisms, such as thermal relaxation, may also occur,but are generally considered undesirable.

The initial OLEDs used emissive molecules that emitted light from theirsinglet states (“fluorescence”) as disclosed, for example, in U.S. Pat.No. 4,769,292, which is incorporated by reference in its entirety.Fluorescent emission generally occurs in a time frame of less than 10nanoseconds.

More recently, OLEDs having emissive materials that emit light fromtriplet states (“phosphorescence”) have been demonstrated. Baldo et al.,“Highly Efficient Phosphorescent Emission from OrganicElectroluminescent Devices,” Nature, vol. 395, 151-154, 1998;(“Baldo-I”) and Baldo et al., “Very high-efficiency green organiclight-emitting devices based on electrophosphorescence,” Appl. Phys.Lett., vol. 75, No. 3, 4-6 (1999) (“Baldo-II”), which are incorporatedby reference in their entireties. Phosphorescence is described in moredetail in U.S. Pat. No. 7,279,704 at cols. 5-6, which are incorporatedby reference.

FIG. 1 shows an organic light emitting device 100. The figures are notnecessarily drawn to scale. Device 100 may include a substrate 110, ananode 115, a hole injection layer 120, a hole transport layer 125, anelectron blocking layer 130, an emissive layer 135, a hole blockinglayer 140, an electron transport layer 145, an electron injection layer150, a protective layer 155, and a cathode 160. Cathode 160 is acompound cathode having a first conductive layer 162 and a secondconductive layer 164. Device 100 may be fabricated by depositing thelayers described, in order. The properties and functions of thesevarious layers, as well as example materials, are described in moredetail in U.S. Pat. No. 7,279,704 at cols. 6-10, which are incorporatedby reference.

More examples for each of these layers are available. For example, aflexible and transparent substrate-anode combination is disclosed inU.S. Pat. No. 5,844,363, which is incorporated by reference in itsentirety. An example of a p-doped hole transport layer is m-MTDATA dopedwith F.sub.4-TCNQ at a molar ratio of 50:1, as disclosed in U.S. PatentApplication Publication No. 2003/0230980, which is incorporated byreference in its entirety. Examples of emissive and host materials aredisclosed in U.S. Pat. No. 6,303,238 to Thompson et al., which isincorporated by reference in its entirety. An example of an n-dopedelectron transport layer is BPhen doped with Li at a molar ratio of 1:1,as disclosed in U.S. Patent Application Publication No. 2003/0230980,which is incorporated by reference in its entirety. U.S. Pat. Nos.5,703,436 and 5,707,745, which are incorporated by reference in theirentireties, disclose examples of cathodes including compound cathodeshaving a thin layer of metal such as Mg:Ag with an overlyingtransparent, electrically-conductive, sputter-deposited ITO layer. Thetheory and use of blocking layers is described in more detail in U.S.Pat. No. 6,097,147 and U.S. Patent Application Publication No.2003/0230980, which are incorporated by reference in their entireties.Examples of injection layers are provided in U.S. Patent ApplicationPublication No. 2004/0174116, which is incorporated by reference in itsentirety. A description of protective layers may be found in U.S. PatentApplication Publication No. 2004/0174116, which is incorporated byreference in its entirety.

FIG. 2 shows an inverted OLED 200. The device includes a substrate 210,a cathode 215, an emissive layer 220, a hole transport layer 225, and ananode 230. Device 200 may be fabricated by depositing the layersdescribed, in order. Because the most common OLED configuration has acathode disposed over the anode, and device 200 has cathode 215 disposedunder anode 230, device 200 may be referred to as an “inverted” OLED.Materials similar to those described with respect to device 100 may beused in the corresponding layers of device 200. FIG. 2 provides oneexample of how some layers may be omitted from the structure of device100.

The simple layered structure illustrated in FIGS. 1 and 2 is provided byway of non-limiting example, and it is understood that embodiments ofthe invention may be used in connection with a wide variety of otherstructures. The specific materials and structures described areexemplary in nature, and other materials and structures may be used.Functional OLEDs may be achieved by combining the various layersdescribed in different ways, or layers may be omitted entirely, based ondesign, performance, and cost factors. Other layers not specificallydescribed may also be included. Materials other than those specificallydescribed may be used. Although many of the examples provided hereindescribe various layers as comprising a single material, it isunderstood that combinations of materials, such as a mixture of host anddopant, or more generally a mixture, may be used. Also, the layers mayhave various sublayers. The names given to the various layers herein arenot intended to be strictly limiting. For example, in device 200, holetransport layer 225 transports holes and injects holes into emissivelayer 220, and may be described as a hole transport layer or a holeinjection layer. In one embodiment, an OLED may be described as havingan “organic layer” disposed between a cathode and an anode. This organiclayer may comprise a single layer, or may further comprise multiplelayers of different organic materials as described, for example, withrespect to FIGS. 1 and 2.

Structures and materials not specifically described may also be used,such as OLEDs comprised of polymeric materials (PLEDs) such as disclosedin U.S. Pat. No. 5,247,190 to Friend et al., which is incorporated byreference in its entirety. By way of further example, OLEDs having asingle organic layer may be used. OLEDs may be stacked, for example asdescribed in U.S. Pat. No. 5,707,745 to Forrest et al, which isincorporated by reference in its entirety. The OLED structure maydeviate from the simple layered structure illustrated in FIGS. 1 and 2.For example, the substrate may include an angled reflective surface toimprove outcoupling, such as a mesa structure as described in U.S. Pat.No. 6,091,195 to Forrest et al., and/or a pit structure as described inU.S. Pat. No. 5,834,893 to Bulovic et al., which are incorporated byreference in their entireties.

Unless otherwise specified, any of the layers of the various embodimentsmay be deposited by any suitable method. For the organic layers,preferred methods include thermal evaporation, ink-jet, such asdescribed in U.S. Pat. Nos. 6,013,982 and 6,087,196, which areincorporated by reference in their entireties, organic vapor phasedeposition (OVPD), such as described in U.S. Pat. No. 6,337,102 toForrest et al., which is incorporated by reference in its entirety, anddeposition by organic vapor jet printing (OVJP), such as described inU.S. patent application Ser. No. 10/233,470, which is incorporated byreference in its entirety. Other suitable deposition methods includespin coating and other solution based processes. Solution basedprocesses are preferably carried out in nitrogen or an inert atmosphere.For the other layers, preferred methods include thermal evaporation.Preferred patterning methods include deposition through a mask, coldwelding such as described in U.S. Pat. Nos. 6,294,398 and 6,468,819,which are incorporated by reference in their entireties, and patterningassociated with some of the deposition methods such as ink jet and OVJP.Other methods may also be used. The materials to be deposited may bemodified to make them compatible with a particular deposition method.For example, substituents such as alkyl and aryl groups, branched orunbranched, and preferably containing at least 3 carbons, may be used insmall molecules to enhance their ability to undergo solution processing.Substituents having 20 carbons or more may be used, and 3-20 carbons isa preferred range. Materials with asymmetric structures may have bettersolution processibility than those having symmetric structures, becauseasymmetric materials may have a lower tendency to recrystallize.Dendrimer substituents may be used to enhance the ability of smallmolecules to undergo solution processing.

Devices fabricated in accordance with embodiments of the invention maybe incorporated into a wide variety of consumer products, including flatpanel displays, computer monitors, televisions, billboards, lights forinterior or exterior illumination and/or signaling, heads up displays,fully transparent displays, flexible displays, laser printers,telephones, cell phones, personal digital assistants (PDAs), laptopcomputers, digital cameras, camcorders, viewfinders, micro-displays,vehicles, a large area wall, theater or stadium screen, lightingfixtures, or a sign. Various control mechanisms may be used to controldevices fabricated in accordance with the present invention, includingpassive matrix and active matrix. Many of the devices are intended foruse in a temperature range comfortable to humans, such as 18 degrees C.to 30 degrees C., and more preferably at room temperature (20-25 degreesC.).

The materials and structures described herein may have applications indevices other than OLEDs. For example, other optoelectronic devices suchas organic solar cells and organic photodetectors may employ thematerials and structures. More generally, organic devices, such asorganic transistors, may employ the materials and structures.

As used herein, a “fuse” may refer to a component that is electricallyconductive under normal operation, but when an excess current flowsthrough the fuse, it generates enough heat to burn the fuse (orotherwise open an electrical circuit). Excess current could be causedby, for example, a current surge from the mains or by the application ofexcess current from the source. In some instances, excess current couldarise from the application of reverse current to the device or couldarise upon the occurrence of a short circuit. The above are provided asexamples and are not meant to be limiting. In general, there may bevarious causes of electrical shorts. These include, but are not limitedto, locally high electric fields caused by variations in the thicknessof the organic stack, conductive spikes on the TCO surface, and/orpinholes in the cathode layer or particulate contamination inside theorganic stack, on the electrode surfaces, or arising from conductive buslines. Electrical shorts may also arise, for instance, because ofincomplete coverage of an insulating layer (such as a grid layer), suchthat there is a local low resistance path between the electrodes. Thus,as used in this context, a fuse may open an electrical connection inresponse to excess current that may arise from some or all of thesecauses, or any other cause.

As noted above, a fuse may open an electrical connection or circuit inany suitable manner. For example, a fuse may burn or may otherwise openan electrical circuit such as by melting, ablating, cracking, orundergoing any other chemical or physical change that prevents the flowof current through the fuse. Thus, as may be appreciated by one of skillin the art, there are many possible mechanisms by which a fuse may openan electrical connection in accordance with embodiments disclosedherein.

As used herein, an “excess current” may refer to an amount of currentthat is greater than the maximum current flowing through a fuse duringnormal operation, such as the amount of current that occurs in responseto a short circuit and/or a reverse current of any magnitude. The amountof current at which point the fuse opens the electrical connection maybe referred to as the “melting current” of the fuse. As used herein, the“cross-sectional area” of a fuse may refer to the area of a crosssection of the fuse that is substantially perpendicular to the directionof current flow through the fuse.

Although the current at which the fuse opens an electrical connectionmay be referred to herein as the “melting current,” it should beunderstood that there are many possible mechanisms by which a fuse mayopen an electrical connection other than melting or ablating the fuse.Some examples of such mechanisms were provided above. Therefore, aswould be understood by one of ordinary skill in the art, the “meltingcurrent” for a fuse may generally refer to the current at which the fuseopens an electrical connection, regardless of the manner in which thisis achieved.

As used herein, the term “approximately” may refer to plus or minus 10percent, inclusive. Thus, the phrase “approximately 10 μm” may beunderstood to mean from 9 μm to 11 μm, inclusive.

FIG. 3(a) shows a basic depiction of an OLED 300. In general, an OLEDmay include a light emitting device that utilizes thin films 301 oforganic material placed between two electrodes 302 and 303. As notedabove, the organic material layers 301 may be very thin (for example, onthe order of 100-200 nm), and therefore any rough surface features,embedded particles, or other imperfections may cause the two electrodes302 and 303 to electrically connect to each other so as to form a shortcircuit due to the particular imperfection. Once this occurs, most ofthe current (or a significantly larger portion of the current) that issupplied to the OLED may flow through the shorted location because ofits relatively low resistance, thereby leaving little if any current (ora significantly less portion of current) to flow through the rest of theorganic layers 301 to generate light. That is, for example, when a shortoccurs, additional current (i.e. an amount of current that may exceedthe maximum current during normal operations) may begin to flow throughthe portion of the OLED where the short occurs, rather than throughother portions of the EL material of the OLED, and thereby reduce theamount of light generated by the device (or by a portion of the device).This may cause the whole device to fail.

The occurrence of a short(s) in a portion of an OLED is typically not aproblem for devices such as active-matrix organic light emitting diode(AMOLED) displays where each display pixel may be isolated from the restof the pixels through complicated circuits. Thus, in these devices, oneshort may not cause the rest of the display to fail (or to otherwisesignificantly decrease the amount of current that flows through otherportions of the device, which may otherwise decrease the amount of lightemitted from the device). However, this type of shorting does present asignificant problem for many implementations of OLEDs (such as lightingpanels), where there may be a general preference to use simplelarge-pixel designs (e.g. where the pixels may not be individuallyaddressable) so as to minimize the cost of fabricating the devices (forexample, by reducing the number of fabrications steps and/or decreasethe number of components and circuitry included in the device). In theseand similar applications, one short fault may fail the whole device ormay cause enough of the device to fail (or otherwise reduce the amountof light emitted from the device and/or portions thereof) that it would,for practical purposes, render the device unusable for its intendedpurpose and/or create a noticeably degraded performance.

That is, for example, a short may be more problematic in OLED devicessuch as passive matrix organic light emitting diode (PMOLED) displaysthan in AMOLED displays because the lines and columns in the PMOLED maybe used to address individual pixels. Therefore, in these devices, ashort in one pixel may cause all of the pixels on the same display lineto be inoperable, while pixels on other display lines may continue tooperate unaffected. Therefore, a short in such a device may create anoticeable decrease in performance because of the multiple pixels oneach display line that may be affected by a single short. A short may bemost problematic in OLED devices where the pixels may be commonlyaddressable and not individually addressable. In such devices, one shortmay affect the performance of all (or substantially all) of the otherpixels, and may thereby render such a device unusable or ineffective orits intended purpose.

This short fault problem may be generally described in more detail withfurther reference to FIG. 3. For purposes of explanation, FIG. 3(a) isdescribed in the context of a simple bottom emission OLED 300. However,it should be understood that the principles and embodiments discussedherein may be equally applicable to any type of OLED, including topemission OLEDs, SOLEDs, TOLEDs, inverted OLEDs, and/or any othercombination of organic devices. In the example of a bottom emissionOLED, the exemplary device 300 in FIG. 3 may include a transparent anode302 comprising material such as ITO (or another transparent conductivematerial) and a cathode 303 comprising a material such as Al. However,as one of ordinary skill in the art would understand, any suitablematerial may be used for the anode 302 and cathode 303.

With reference to FIG. 3(b), a top view of an equivalent circuit of anOLED light panel is shown. The arrows 305 indicate the current flowdirection of the device (as shown, from the anode 302 to the cathode 303through the EL layer 301). Continuing with the exemplary embodiment andmaterials discussed above, the resistance of the Al in the cathode 303may be very low in comparison to the resistance of the ITO thatcomprises the anode 302 and therefore will be omitted for purposes ofthis illustration.

In general, the resistance of ITO should be considered in a large OLEDpixel (for example, a pixel having dimensions greater than 2 cm×2 cm).This resistance is represented by resistors 304 in the equivalentcircuits in FIGS. 3(b) and (c). For purposes of this example, the ITOresistance in the vertical dimension of the anode 305 is omitted forsimplicity. In the configurations shown in FIGS. 3(b) and (c), thecurrent may flow along the ITO anode 302 (to the right in FIG. 3(b)) andthrough the organic EL material 301 to the cathode plane 303 (in theupward direction in FIG. 3(b)). For purposes of the discussions herein,it may be assumed that the amount of current flowing though each portionof the OLED is relatively uniform when no fault has occurred; however,those of skill in the art would recognize that there may be somevariation in the amount of current that flows through different portionsof the OLED panel 300 based on, for instance, the sheet resistance ofthe anode, the distance from the current or voltage source, and/or otherimperfections of the device and layers thereof. This non-uniformity maybe considered for practical implementations of any device, as would beunderstood and appreciated by one of ordinary skill in the art.

As shown in FIG. 3(b), the exemplary equivalent circuit is shown ascomprising an 8×6 matrix of diodes 306 with 8 rows and 6 columns innormal operation. Each diode 306 may represent a separate OLED circuitelement. FIG. 3(c) shows a top view of the equivalent circuit of an OLEDpanel represented by an 8×6 matrix of diodes under a fault condition.When a short occurs, for instance at the position 307, an increasedcurrent may flow through the ITO anode 302 to the shorted spot 307, andthen continue to the cathode 303, as shown in FIG. 3(c). In this case,no current (or an insufficient amount of current to illuminate the OLEDpanel to a desired or needed level) may pass through the other OLEDcircuit elements in the rest of the device and therefore the occurrenceof a single short may cause the whole panel to fail, or enough of thedevice to fail that it would, for practical purposes, be unusable or mayhave noticeably degraded performance.

One potential solution to this shorting problem contemplated by some ofthe embodiments disclosed herein is to divide the large size lightingpanel into smaller segments (e.g. “pixels”), and then incorporate fusesat each individual pixel. The fuses may be configured so as to open anelectrical circuit in response to an excess current, such as when ashort circuit occurs. For instance, once a potential short startsdrawing a large current, the fuse may open and isolate the shorted pixelfrom the rest of the panel. Some embodiments may also permit shorttolerance for faults that may occur at locations other than within aparticular pixel. In some embodiments, the pixels may be designed orconfigured to be very small so that the shorted region will notnoticeably affect the appearance or the function of the whole firstdevice. That is, if a pixel or a small number of pixels are isolated viaa fuse because of an excess current, the region of the device affectedby these pixels may be small enough such that the OLED may stillfunction for its intended purpose.

The inventors have found that, with regard to some embodiments (such asthose used in applications such as lighting devices), the size of thepixels may be designed based on factors and requirements that improvethe performance of the device while minimizing or reducing the effectsof any shorts that may develop within the device. For example, the sizeof the pixels may be chosen to increase the brightness uniformity acrossthe device, to improve the overall aesthetics of the device, or may begenerally chosen based on fill factor or other manufacturing conditions.This may be in contrast to the selection of pixel size in AMOLED andPMOLED displays, where the size of the pixels is generallypre-determined based on the display resolution. That is, the number ofpixels and thereby the size of each of the pixels is generally chosenbased on the maximum resolution of the display. Moreover, unlikedisplays where each pixel may be individually addressed so as togenerate an image, the pixels corresponding to some embodiments (such aslighting devices or similar applications) may be electrically connectedtogether such that they are commonly addressable. This may therebyreduce manufacturing costs, the amount and complexity of any addressingcircuitry, and/or the overall number of components needed to operate thedevice. Although the inventors have found that pixelating a lightingdevice may offer some advantages in some embodiments (including designchoices regarding the pixels themselves), it should be appreciated thatthe features, concepts, and embodiments of the short tolerant structuresdisclosed herein may also be applicable to display embodiments.

In addition to the short fault problem discussed above, in someembodiments that may include a fuse at each individual pixel level mayalso be tolerant to excess current in the device, or in the individualpixel, that are caused by other factors. In particular, some embodimentsmay prevent excess current flow through a pixel that may otherwisedamage or affect the performance of the device by opening an electricalcircuit in response to the excess current and electrically isolating thepixel. Some examples of such causes of excess current were providedabove; however, the fuses in some embodiments may open a circuit inresponse to any excess current, regardless of its source or cause.

A first device may be provided that includes a short tolerant structure.The first device may include a substrate and a plurality of OLED circuitelements disposed on the substrate. The substrate may contact either theanode or the cathode of the first device. The substrate may be lighttransmissive (e.g. transparent or semi-transparent) or it may be opaque.For embodiments where the substrate is light transmissive, the substratemay comprise a material such as transparent glass or plastic. However,any material that is light transparent and is suitable for use in anOLED may be used. In some embodiments, the substrate may be opaque andmay comprise materials such as glass, plastic, semi-conductor materials,silicon, ceramics, and/or circuit board materials. However, any materialthat is suitable for OLED devices may be used. Furthermore, thesubstrate may be rigid or flexible. A flexible substrate may provide foran increase functionality, such as by providing for use in devices thatmay be disposed in unique locations (e.g. lighting panels around cornersor disposed inside containers or other vessels) or that may be morecompact and transportable.

As used in this context, each of the “OLED circuit elements” includesone, and only one, pixel. The use of the open-ended claim language“comprising” along with the phrase “one and only one” to describe thepixel means that each OLED circuit element includes only a single pixel,but may include a variety of other items such as fuses, conductors,resistors, etc. As used in this context, a “pixel” may include a firstelectrode, a second electrode, and an organic electroluminescent (EL)material disposed between the first and the second electrodes. The pixelof each of the OLED circuit elements may include a bottom or topemission organic light emitting diode, a stacked organic light emittingdiode (SOLED), a transparent organic light emitting diode (TOLED), aninverted organic light emitting diode, and/or any othervariation/combination of OLED. In general, each pixel may have at leastone of either the first electrode, second electrode, and/or an organiclayer that has been patterned such that the patterned elements are notcommon or shared with any other pixel. The patterned component of apixel may be either the first electrode or the second electrode. Thepixel of each of the OLED circuit elements may correspond to the activearea of the device from which light is emitted. In some embodiments(examples of which are described herein), in the first device asdescribed above, a short in one pixel may not prevent the other pixelsof the device from functioning properly—or from enabling the firstdevice to continue to perform its intended function.

As would be appreciated by one of skill in the art, the patternedelectrode of each pixel may be physically segmented from thecorresponding patterned electrode of each of the other pixels, but thismay not necessarily mean that each pixel is physically isolated (i.e.that each pixel comprises a separate electrical “island”). That is, forexample, in some embodiments, a fuse that connects to a patternedelectrode may also connect to a common bus line or may otherwise“physically connect” two patterned electrodes together (either directlyor via other components of the device). In general, as would beunderstood by one of ordinary skill in the art, reference to “physicalseparation” or “physical segmentation” of the electrode of each pixelmay refer to when the electrodes are pixilated such that if a fuse opensan electrical circuit corresponding to the electrode, current will nolonger flow through the pixel that includes that particular electrode,but current may still through the other pixels of the device.

The OLED circuit elements may also include a fuse. The fuse or fuses ofthe OLED circuit elements may be adapted to open an electricalconnection in response to an excess current in the pixel (or an excesscurrent in a portion of the device that is near the pixel). A fuse maybe configured to operate according to any suitable method including, butnot limited to, ablation of the fuse in response to a short circuit. Ifan excess current occurs in one of the OLED circuit elements, theincreased current through the OLED circuit element may cause the fuse toopen the circuit, thereby converting the short failure to an openfailure. In this manner, in some embodiments, the OLED circuit elementmay thereby be electrically isolated from the other components of thefirst device. In some embodiments, each of the OLED circuit elements maynot be electrically connected in series with any other of the OLEDcircuit elements. In this manner, when an OLED circuit element failsopen (i.e. when a fuse isolates the OLED circuit element or componentsthereof), current still flows to the other OLED circuit elements in thefirst device.

As would be understood by a person of ordinary skill in the art, othersuitable methods for a fuse to operate may include, by way of exampleonly, melting, burning, ablating, cracking or chemical or physicalmodification of fuse in response to a short circuit.

The parameters of a fuse that may be used in embodiments disclosedherein, such as materials and dimensions, may be readily selected by oneof skill in the art to accommodate a desired normal operating current,melting current, and short circuit current. An example of this isdiscussed below. As used herein, a “short circuit current” may refer tothe current that flows through a device when a short circuit occurs inthe absence of a fuse. As used herein, the “melting current” may referto the minimum current at which the fuse is designed to open, and ispreferably less than the short circuit current but greater than themaximum operating current. A person of ordinary skill in the art wouldknow how to select parameters of the fuse to accommodate desired ordesigned maximum operating current, minimum short circuit current, andmelting current. An example of this is described below with reference toFIG. 21. In general, the properties of the fuse should be such that thefuse is electrically conductive under normal operation, but when anexcess current begins to flow through (or near) the OLED circuitelement, the excess current passing through the fuse generates enoughheat to burn or ablate the fuse (or otherwise cause the fuse to open)and thereby open the electrical connection.

In some embodiments, a particular dimension or dimensions of the fusemay have a greater or lesser effect on the amount of current that maypass through the fuse without the fuse opening the electricalconnection. For example, in embodiments where the fuse comprises aportion of a blanket thin layer or when an electrode of an OLED circuitelement comprises the fuse. The “thickness” of the fuse in suchembodiments may be a factor that determines the amount of current thatwill open the circuit (i.e. it may be a factor in establishing themelting current of the fuse). Examples of such embodiments areillustrated in FIGS. 4, 5, and 12 and described with respect to the“exemplary embodiments” identified below as embodiments 1, 2, and 5.

In some embodiments, the cross-sectional area may be a significantfactor that determines the amount of current that will open the circuit(i.e. the melting current of the fuse). Examples of such embodiments areillustrated in FIGS. 6 and 7 and described with respect to theidentified “exemplary embodiments” 3 and 4 below.

In general, a more conductive (less resistive) material may act as afuse for given current levels at smaller dimensions than a lessconductive material. This may be due, in part, to the decrease inresistivity of the more conductive material, where the heat generated bya current passing through the fuse is based at least in part on theresistivity of the material of the fuse (i.e. the joule heating in thefuse is proportional to the amount of square of the current (I) timesthe resistance of the fuse (R)). Any material and any dimensions of afuse are contemplated herein so long as the component functions properlyas a fuse in the OLED.

As noted above, one of skill in the art may readily select parameters ofthe fuse (such as the materials and dimensions of the fuse) based on thenormal operating current and the expected or predicted short circuitcurrent so as to provide a fuse having melting current such that thefuse is designed to open the electrical connection at a desired currentin relation to the maximum operating current. Preferably, the meltingcurrent of the fuse may be greater than the normal operating current,and preferably less than or equal to the short circuit current. Bydesigning the fuse to conduct electricity at (and preferably slightlyabove) the normal operating current, but below the short circuitcurrent, embodiments may provide for a device that operates normallywhen a short does not occur but will isolate a portion of the device ifa short occurs (or begins to occur).

As would be appreciated by one of skill in the art, for a device thatmay have multiple normal operating currents (such as a dimmable device),the “normal operating current” that may be used to determine the designparameters of the fuse may correspond to the maximum operating currentof the device. In this manner, a fuse may be designed such that it willnot open when the device is operating at the highest brightness level ofthe device.

As noted above, some embodiments may comprise a plurality of pixels eachcomprising a fuse. If one of the fuses is opened, then in someinstances, there may be an increase in current that flows through theother OLED circuit elements during normal operation. Therefore, it maybe preferred, in some embodiments, that the fuse has a melting currentthat takes this increase current during normal operation intoconsideration. However, if the fuse has a melting current that is setabove the short circuit current, when a short occurs, the fuse may notopen and thereby the device may be rendered inoperable. Depending uponthe specific application of the device, it may be desirable to have ahighly sensitive fuse that opens in response to a current that is onlyslightly higher than the maximum operating current, or it may bedesirable to have a less sensitive fuse that allows a significant excesscurrent to flow prior to opening the fuse. For example, it may bepreferred that the fuse opens in response to an excess current that is10%, 50%, 100%, 200%, or even 400% greater than the maximum operatingcurrent. Where there is a range of operating currents (for example, suchthat the luminance of the OLED light panel may be controlled), themelting current of the fuse should be greater than the maximum operatingcurrent (i.e. the current that is provided when the device is operatingat its highest current at which the device is designed to operate). Themelting current of the fuse may also be designed to be less than theminimum short circuit current (i.e. the current that is provided whenthere is an electrical short when the device is operating at its lowestcurrent at which the device is designed to operate).

In some embodiments, the OLED circuit elements may include various othercomponents and circuitry in addition to a fuse and the one pixel. Forinstance, an OLED circuit element may contain additional resistors,capacitors, inductors, voltage/current metering devices, voltage/currentsources, diodes, transistors, and/or additional fuses. However, as usedherein and noted above, an “OLED circuit element” includes only onepixel. Additional circuit components not listed may also be included.Furthermore, a plurality of OLED circuit elements may share a commoncircuit component. For instance, in some embodiments multiple OLEDcircuit elements may share a common unpatterned layer such as anunpatterned electrode or organic layer. Additionally, in someembodiments, a portion of the fuse of an OLED circuit element may alsocomprise a portion of a fuse of another OLED circuit element. Anexemplary embodiment where a portion of a fuse may be shared isillustrated in FIG. 5 and described in more detail below. In thatexemplary embodiment, a portion of the top conductive layer may beablated if an excess current flows through one pixel (such as when ashort occurs in the pixel) and may also be ablated if an excess currentflows in an adjacent pixel. However, as defined herein, a pixel (asdefined herein) may not be common to multiple OLED circuit elements.

Although embodiments may describe fuses that open an electrical circuitbased on a particular method (such as ablation of the fuse), as notedabove, fuses may in general open an electrical circuit in any suitablemethod. Thus, in the above exemplary embodiment, it would be appreciatedthat the top conductive layer could open an electrical connection inresponse to an excess current in accordance with any of these knownmethods.

In some embodiments, the fuse may be separable from the pixel (i.e. afirst electrode, a second electrode, and an organic layer), and the fusemay be connected in series with the pixel of each of the OLED circuitelements. When an excess current flows through the pixel (and therebythe fuse because of the series connection), it may cause the fuse toopen. Moreover, because the fuse is in series with the pixel, the excesscurrent cannot continue to flow through the pixel after the fuse opensthe electrical connection.

In some embodiments, where the first device comprises a plurality ofOLED circuit elements, the first or the second electrode in each of theplurality of OLED circuit elements may be the fuse. That is, forinstance, the first or the second electrode may be designed orconfigured to comprise parameters such that it will open an electricalconnection in response to an excess current (which as noted above, maybe set in accordance with the particular design and purpose of thedevice, such as 10%, 20%, 50% 200%, or 400% greater than the normal ormaximum operational current). Example embodiments where the first or thesecond electrode may comprise a fuse are shown in FIGS. 4 and 12 anddescried herein. The first or the second electrode that comprises a fusemay open an electrical connection in response to an excess current inaccordance with any known method, including by way of example, the firstor second electrode may be ablated in response to an excess current.

As described above, in general when a fuse is opened, it causes a shortfault to become an open fault and current is thereby prevented fromflowing through the shorted pixel. For some embodiments where the firstor the second electrode is a fuse, the electrode may have a thicknesssuch that, in response to an excess current in the OLED circuit element,the electrode is ablated. In such embodiments, the thickness of theelectrode may refer to the dimension of the electrode that is along theaxis that is substantially perpendicular to the plane of the substrate.The thickness of an electrode that functions as a fuse may be a functionof such conditions and parameters as the electrode material, the normaldevice operating current, and the short-circuit current (i.e. thecurrent that will flow through the electrode if a short occurs). Anymaterial and thickness may be used as would be understood by one ofordinary skill in the art so long as the electrode functions as a fuseat a desired melting current. For example, the inventors have found thatfor some embodiments, the electrode may have a thickness between 1 nmand 60 nm and/or the material may be a conductive metal such asaluminum.

In some embodiments, the first device as described above, may be a signor a lighting panel or it may be a consumer device such as a lightfixture. As used herein, a “light fixture” may comprise any one of, orsome combination of any of the following: a light source or lamp; areflector; an aperture; a lens; a power supply; a connection to a powersource; and/or a light socket to hold the lamp. Although embodiments maybe particularly applicable to such commercial devices because theselighting devices may, for instance, not comprise individuallyaddressable pixels and/or other advance circuitry, embodiments are notso limited. Indeed, embodiments and the concepts/features describedherein may be used in any suitable OLED.

In some embodiments, the pixel of each of the OLED circuit elements ofthe first device as described above may have a surface area betweenapproximately 0.001 and 5.0 cm². As used in this context, the “surfacearea of the pixel” may be a measure of a surface area of the first orthe second electrode. Preferably, the surface area is the measure of thesurface area of a patterned electrode of the pixel (that is, anelectrode that may not be common to a plurality of other OLED pixels).In some embodiments, the surface area of the first or second electrodeis the area of the surface of the electrode that is substantiallyparallel to the substrate. For example, with reference to FIG. 3(a), thesurface area may be the measure of the top surface of the electrode 303.In general, the inventors have found that for an electrode (particularlyin embodiments where the electrode may comprise a fuse) having a surfacearea larger than approximately 5.0 cm² may result in unnecessarily highresistive loses for the OLED. In addition, the inventors have found thatin some embodiments, an electrode having a surface area smaller thanapproximately 0.001 cm² may unnecessarily increase fabrication cost anddecrease fill factor. Thus, in some embodiments, the electrode may havea surface area that is between approximately 0.001 cm² and 5.0 cm².

As would be appreciated by one of skill in the art, the reference aboveto the “surface area” of the pixel may relate to the emissive area ofthat particular pixel, where the emissive area would be understood to bethe relevant portion of the pixel in determining the contribution of thetotal light emissions of the device that is provided by each pixel. Thatis, the “emissive area” of a pixel may be a measure of a surface area ofthe pixel for which charge injection from opposing electrodes andsubsequent recombination of charge and light emission is enabled. Thus,for instance, in some embodiments, it may be preferred that the emissivearea is between approximately 0.001 and 5.0 cm². In general, theinventors have found that for a pixel (particularly in some embodimentswhere the electrode of that pixel may comprise a fuse) having anemissive area larger than approximately 5.0 cm² may result inunnecessarily high resistive loses for the OLED. In addition, theinventors have found that in some embodiments, a pixel having anemissive area smaller than approximately 0.001 cm² may unnecessarilyincrease fabrication cost and decrease fill factor. Thus, in someembodiments, the pixels may have an emissive area that is betweenapproximately 0.001 cm² and 5.0 cm².

Similarly, in some embodiments, the emissive area of the pixel of eachof the plurality of OLED circuit elements may comprise no more thanapproximately 10% of the emissive area of the first device. In someembodiments, the emissive area of the pixel of each of the plurality ofOLED circuit elements may comprise no more than approximately 1% of theemissive area of the first device. As noted above, the smaller theemissive area of each pixel, the less impact a non-emitting pixel willhave on the overall emission (and thereby the performance of thedevice).

In some embodiments, in the first device as described herein, the firstdevice may include at least 10 OLED circuit elements. In someembodiments, it may be preferred that the surface area of the pixel ofeach of the OLED circuit elements comprises no more than 10% of thesurface area of the first device. In this manner, if one of the pixelsdevelops a short and thereby a fuse is opened to electrically isolatethat pixel, approximately 10% or less of the surface area of the firstdevice will no longer emit light. This may be a small enough percentageof the device such that it may continue to function adequately for itsintended purpose (such as a lighting panel that may continue to providelight to an area). As used in this context, the surface area of thefirst device may be a measure of the surface area of the portion of thesubstrate that is common to a plurality of pixels. In some instances,the surface area of the device may be the measure of the combinedsurface area of the pixel of each of the plurality of OLED circuitelements (where the surface area of the pixel was defined above). Asnoted above, the smaller the number of OLED circuit elements in a deviceand/or the greater the percentage of the surface area of a devicecontributable to a single OLED circuit element may result in a devicewhere a short in a small number of OLED circuit elements causes anundesirably large portion of the device to cease emitting light. Thus,in general, it may be desirable to have a larger number of OLED circuitelements such that each OLED circuit elements comprises a smallerpercentage of the total surface area of the device (and thereby providesa smaller percentage of the total amount of light that is emitted fromthe device).

As noted above and as would be appreciated by one of skill in the art,the reference above to the “surface area” of the pixel may relate to theemissive area of that particular pixel, where the emissive area would beunderstood to be the relevant portion of the pixel in determining thepercentage of the total light emissions of the device that is providedby each pixel. Thus, for instance, in some embodiments, it may bepreferred that the emissive area of the pixel of each of the OLEDcircuit elements comprises no more than 10% of the total emissive areaof the first device. In this manner, if one of the pixels develops ashort and thereby a fuse is opened to electrically isolate that pixel,approximately 10% or less of the total emissive area of the first devicewill no longer emit light. This may be a small enough percentage of thedevice such that it may continue to function adequately for its intendedpurpose (such as a lighting panel that may continue to provide light toan area). The “total emissive area” of the first device may be a measureof the combined emissive area of the pixel of each of the plurality ofOLED circuit elements (where the emissive area of the pixel wasdescribed above). As noted above, a smaller number of OLED circuitelements in a device and/or a greater percentage of the emissive area ofa device contributable to a single OLED circuit element may result in adevice where a short in a small number of OLED circuit elements causesan undesirably large portion of the device to cease emitting light.Thus, in general, it may be desirable to have a larger number of OLEDcircuit elements such that each OLED circuit element comprises a smallerpercentage of the total emissive area of the device (and therebyprovides a smaller percentage of the total amount of light that isemitted from the device).

In some embodiments, in the first device as described herein, the firstelectrode of each pixel may be patterned such that it is physicallyseparate from the first electrode of the pixel of each of the other OLEDcircuit elements. Patterning may be performed by any known methodincluding deposition through a mask, cold welding, and/or patterningassociated with some of the deposition methods mentioned above includingink jet and OVJP. Other methods may also be used. In some embodiments,the second electrode of each pixel may be unpatterned such that thesecond electrode is common to a plurality of pixels. This may decreasemanufacturing costs by reducing the number of fabrication steps and/ordecrease the number of electrical components and connections that areneeded for the device. In some embodiments, the first electrode may bean anode and the second electrode is a cathode; however, embodiments arenot so limited, and in some instances, the first electrode may be acathode and the second electrode is an anode.

As noted above and would be appreciated by one of skill in the art, thepatterning of an electrode such that a plurality of physically separateelectrodes are formed that may correspond to each of the pixels does notnecessarily mean that each electrode is physically isolated (i.e. thateach electrode or pixel comprises a separate electrical “island”). Theelectrodes may be physically separate components, but may be connectedvia one or more components, such as through a fuse.

In some embodiments, the second electrode (which may be unpatterned insome embodiments) may be disposed over the substrate, the organic ELmaterial may be disposed over the second electrode, and the firstelectrode may be patterned and disposed over the organic EL material.Examples of such embodiments are shown in FIGS. 4(a)-(d), 5(a)-(d), 6,and 12(a)-(d). Other material may be disposed between, over, or under,the first and second electrodes and the EL material. However,embodiments are not so limited, and in some instances the firstelectrode may be patterned and disposed over the substrate, the organicEL material may be disposed over the first electrode, and the secondelectrode may be disposed over the organic EL material. Other materialmay be disposed between, over, or under, the first and second electrodesand the EL material.

In some embodiments, in the first device as described above where thesecond electrode may be disposed over the substrate, the organic ELmaterial may be disposed over the second electrode, and the firstelectrode may be patterned and is disposed over the organic EL material,the first device may further include a plurality of segmented bus lines.The plurality of bus lines may electrically connect the patterned firstelectrode of each of the plurality of OLED circuit elements together.The segmented bus lines may comprise thick, highly conductive stripsthat form electrical interconnects between the first electrodes of thepixel of each of the plurality of OLED circuit elements. In general,because the bus lines may comprise a thick, highly conductive material,they may not transmit light and may result in an inactive area in thefirst device. It should be understood that an “inactive area” may referto a “non-emissive” area of the device (i.e. an area that does not emitlight). Therefore, it may be desirable to limit the amount of spaceoccupied by such components. An example of such an embodiment is shownin FIGS. 4(a)-(d) and described in more detail below.

In some embodiments, in the first device as described above, the firstelectrode of each of the plurality of OLED circuit elements may comprisea fuse such that the first electrode may be configured to open anelectrical connection in response to an excess current in accordancewith any known method, including by way of example, the first electrodemay be ablated in response to a short circuit or an excess current. Asdescribed above, when the fuse opens the circuit, it causes the shortfault to become an open fault and current is thereby prevented fromflowing through the shorted pixel. The use of the first electrode insome embodiments as a fuse may reduce fabrication steps and simplifymanufacturing, as an additional component need not be included thereinto form an electrical connection and also comprise a fuse.

In some embodiments, in the first device as described above where thefirst electrode comprises a fuse, the first electrode may have athickness such that it may conduct current efficiently in normaloperation (i.e. it may create an acceptable amount of resistive powerloss due to the sheet resistance of the material and the current flowingthrough the electrode), yet the first electrode will still open thecircuit should a fault occur (e.g. if an excess current above themelting point (i.e. melting current) flows through the electrode). Asused in this context, the “thickness” of the first electrode may referto the dimension of the electrode that is along the axis that issubstantially perpendicular to the plane of the substrate. Although thefirst electrode may comprise any material and any thickness so long asit functions as a fuse, the inventors have found that a preferred rangeof thicknesses for an electrode comprising aluminum is betweenapproximately 1.0 nm and 60 nm. The inventors have also found that apreferred value for the sheet resistance of the first electrode isbetween approximately 0.1 Ω/sq. and 500 Ω/sq, where the sheet resistanceis a measure of resistance of thin films that are namely uniform inthickness. These parameters were found to both conduct currents duringnormal operations of many exemplary devices, as well as to open anelectrical connection (e.g. by ablating) when a current above thesenormal operating conditions was generated and flowed through theelectrode.

Although with regard to the above examples and exemplary embodiments,reference was made to an electrode comprising aluminum, as would beunderstood by one of ordinary skill in the art, other suitable materialsmay also be used for one or both electrodes. For instance, electrodesmay comprise such materials magnesium and silver alloys (Mg:Ag) or anyother suitable conductive material.

As noted above, in some embodiments the first device may includesegmented bus lines that may be disposed over the first electrode ofeach of the OLED circuit elements. In some embodiments, the segmentedbus lines may be disposed below or between the patterned first electrodeof each of the plurality of OLED circuit elements. In some embodiments,such as when the first electrode of each OLED circuit element comprisesa fuse, the patterned first electrode of each of the OLED circuitelements may be directly connected to less than five segmented buslines. An example of this is shown in FIGS. 4(a)-(d) and describedbelow. In some embodiments, it may be preferred that the segmented buslines are electrically connected to the first electrode of exactly twoof the OLED circuit elements. One potential advantage that someembodiments that utilize segmented bus lines may provide is that theymay be tolerant to faults that may occur in one of the plurality ofsegmented bus lines (i.e. a fault that may not occur within one of thepixels of the device). For instance, if a short fault occurs in somesuch embodiments at one of the plurality of segmented bus lines, theexcess current may flow through the first electrode of one or more ofthe plurality of OLED circuit elements. This excess current may besufficient to ablate the first electrode and thereby cause an opencircuit. As the segmented bus lines may not be electrically connected toany other segmented bus lines in some embodiments, the ablation of thefirst electrodes by the excess current may thereby cause the shortedsegmented bus line to become electrically isolated.

In some embodiments, in the first device as described above where thesecond electrode may be disposed over the substrate, the organic ELmaterial may be disposed over the second electrode, and the firstelectrode may be patterned and disposed over the organic EL material,the first device may further include a thin layer of conductive materialthat electrically connects the patterned first electrode of each of theplurality of OLED circuit elements together. An example of this is shownin FIGS. 5(a)-(d) and described in more detail below. The thickness ofthe thick (i.e. the first patterned electrode) and the thin layer ofconductive material may refer to the dimension of the layer that isdisposed along the axis that is perpendicular to the plane of thesubstrate.

In some embodiments, the thin layer of conductive material may bedisposed over the first electrode (i.e. the thick layer) of each of theplurality OLED circuit elements; however, embodiments are not so limitedand the first electrode of each of the plurality of OLED circuitelements may be disposed over the thin layer of conductive material. Insome embodiments, a portion of the thin layer of conductive material maybe disposed directly on top of the first electrode of each of theplurality of OLED circuit elements, while another portion (or portions)may be disposed over the area of the first device between the firstelectrode of each of the plurality of OLED circuit elements. The thinlayer of conductive material may thereby serve to conduct currentbetween the OLED circuit elements. Again, this is illustrated in theexemplary embodiment shown in FIGS. 5(a)-(d) where the thin layerdisposed directly over the first electrode 501 of the plurality of OLEDcircuit elements is shown as element 502, and the portion of the thinlayer disposed over the area between the first electrodes 501 is shownas element 506.

The thin layer of conductive material may also comprise a fuse in someembodiments. For example, the fuse may comprise the portion of the thinlayer of conductive material that is disposed between, or over, the areaof the first device that is between the first electrode of each of theplurality of OLED circuit elements. The thin layer of conductivematerial may have a thickness such that when an excess current (e.g. acurrent equal to or greater than the melting point of the layer) flowsthrough a portion of the thin layer, that portion is ablated. Forinstance, when a short occurs in the pixel of an OLED circuit element,the excess current may ablate the portions of the thin layer ofconductive material disposed between the first electrode of the shortedOLED circuit element and the first electrode of the other OLED circuitelements. In this manner, the shorted pixel may be electrically isolatedfrom the other pixels of the first device.

As noted above, the patterned first electrode of each pixel in someembodiments may comprise a thick layer of conductive material. Thecharacteristics of the thick layer of conductive material may be chosenso that it may conduct electricity efficiently (e.g. with low resistiveloses) and may not ablate based on an excess current that is less thanthe melting point of the thin layer disposed between the first electrodeof each of the OLED circuit elements. The inventors have found that insome embodiments, a preferred thickness of the thick layer of conductivematerial may be between approximately 10 nm and 500 nm, while thethickness of the thin layer of conductive material may be betweenapproximately 1 nm and 60 nm. In generally, the inventors have foundthat that it may be generally preferred that the thick layer ofconductive material has a thickness that is approximately twice as largeas the thin layer of conductive material. However, any thickness of thethick layer and thin layer of conductive material that enables a portionof the thin layer of conductive material to ablate in response to anexcess current, such when a short occurs, may be utilized.

In some embodiments, each of the OLED circuit elements may comprises athick layer of conductive material and at least a portion of the thinlayer of conductive material (i.e. the first electrode may include boththe thick layer of material and the thin layer of material, which mayhave been deposited over the first electrode; however, in someembodiments, the thick layer and the thin layer of conductive materialmay comprise the same material, and thereby the two layers may comprisethe first electrode). In some embodiments, a fuse may be utilized toelectrically connect the first electrode to the thin conductive layer.

The thin layer of conductive material may be unpatterned in someembodiments. That is, for instance, the unpatterned layer may bedeposited as a blanket layer. However, embodiments are not so limited,and in some instances, the first device may comprise a patterned thinlayer of conductive material that electrically connects the firstelectrode (i.e. the thick layer) of each of the plurality of OLEDcircuit elements together. As noted above, the thick layer of conductivematerial and the thin layer of conductive material may comprise the samematerial. For instance, both the thick layer of conductive material thatcomprises the first electrode and the thin layer of conductive material(that may comprise a fuse) may comprise Al. In some embodiments, thethick layer and thin layer of conductive material may be deposited atthe same time or may be deposited separately. In some embodiments, thematerial for the thick conductive material and the thin conductivematerial may be different.

It should be noted that although reference was made above to a “thick”layer of conductive material (i.e. the electrode) and a “thin” layer ofconductive material, the actual thickness of each of these components(and, correspondingly, the relative thickness of the two layers ofconductive material) may depend on a variety of factors, including thematerial used for each layer. For example, in some embodiments the“thick” and the “thin” conductive layers may have approximately the samethickness (or the “thin” layer may even have a greater thickness thanthe “thick” layer), but the “thin” layer of conductive material maycomprise a material that has a higher resistivity and/or a lower meltingtemperature than the “thick” layer of conductive material. Thus, in theembodiments described above, reference could also be made to a “first”layer (in place of a “thick” layer) of conductive material and a“second” layer (in place of a “thin” layer) of conductive material todescribe the exemplary structures.

To further illustrate the above, in some embodiments in the first deviceas described above, the second electrode may be disposed over thesubstrate, the organic EL material may be disposed over the secondelectrode, a first layer of conductive material (i.e. the “thick layer”as referenced above) may be patterned and disposed over the organic ELmaterial, and a second layer of conductive material (i.e. the “thinlayer” as referenced above) that electrically connects the patternedfirst layer of conductive material of each of the plurality of OLEDcircuit elements together. An example of this is shown in FIGS. 5(a)-(d)and described in more detail below. In some embodiments the first layerof conductive material may have a thickness that is greater than, lessthan, or approximately equal to the thickness of the second layer ofconductive material. The thickness of the first layer (i.e. the firstpatterned electrode) and the second layer of conductive material mayrefer to the dimension of the layer that is disposed along the axis thatis perpendicular to the plane of the substrate.

In some embodiments, the second layer of conductive material maycomprise a fuse. For instance, the second layer may: comprisesubstantially the same material as the first layer, but have a smallerthickness; comprise a different material than the first layer (whetherthe material is more or less conductive than the first layer), and havea smaller thickness than the first layer; comprise a different materialthan the first layer (whether the material is more or less conductivethan the first layer), and have a lower melting temperature than thefirst layer; comprise the same or different material as the first layer(but be less conductive) and have a larger thickness than the firstlayer; or any other suitable arrangement such that the second layer mayopen an electrical connection in response to a short fault.

In some embodiments, in the first device as described above where thesecond electrode may be disposed over the substrate, the organic ELmaterial may be disposed over the second electrode, and the firstelectrode may be patterned and disposed over the organic EL material,the first device may further include a top conductive layer and aninsulating layer. The insulating layer may be disposed over a part ofthe first electrode of each of the plurality of OLED circuit elements,and the top conductive layer may be disposed over the insulator. A fusemay electrically connect the first electrode of each of the plurality ofOLED circuit elements with the top conductor. An example of such anembodiment is shown in FIGS. 6(a)-(d) and described below. Preferably,in some embodiments, the fuse comprises a part of the top conductivelayer. For instance, the fuse may comprise the same material as the topconductive layer and be deposited during the same process and/or at thesame time. This may decrease manufacturing time and expense. However,embodiments are not so limited, and thus the fuse may also comprise adifferent material, which may be based on the desired characteristics ofthe device and/or fuse, such as the desired melting point.

The insulating layer (which may be disposed above the first electrodesbut below the top conductive layer) may be patterned in some embodimentsso as to allow a fuse to connect the top conductor and the firstelectrode of each of the plurality of OLED circuit elements. Forinstance, the insulating layer may comprise a plurality of patternedinsulating segments having a surface area less than a surface area ofthe first electrode of each of the OLED circuit elements. The portion ofthe first electrode that the insulating layer was not disposed directlyover may be electrically connected by a fuse to the top conductivelayer. This is shown in the exemplary embodiment of FIGS. 6(a)-(d).However, it should be understood that any configuration of theinsulating layer that permits the top conductive layer to connect to thefirst electrode through a fuse is contemplated as within the scope ofthis embodiment. In some embodiments, it may be preferred that the topconductive layer is unpatterned so as to reduce fabrication steps andcosts. For instance, the top conductive layer may be a blanket layer.The top conductive layer may also be highly conductive; thereby reducingresistive power losses in the device.

In some embodiments where the flow of current through the fuse issubstantially perpendicular to the plane of the substrate, the fusematerials may comprise a highly conductive metal, such as aluminum(which may be opaque). This may be due, in-part, because the fuse mayhave a small surface area such that it does not block a substantialamount of the active area (i.e. the emissive area) of the OLED circuitelement and thereby need not be transparent. That is, for instance,because the fuse may be made of a highly conductive metal, thecross-sectional area of the fuse may be much smaller than when atransparent conductive oxide (TCO) such as indium tin oxide (ITO) isused and still conduct a sufficient amount of current without openingthe circuit (i.e. because the material may be more conductive, less heatis generated for the same amount of current, and thereby more currentmay flow through the same size fuse without reaching the melting currentof the fuse). In general, there may be greater flexibility in the designof the fuse geometry in such embodiments because there is lesslimitation on the preferred range of the dimensions of the fuse on theaxis that is perpendicular to the current flow direction.

In some embodiments, in the first device as described above, where thefirst electrode may be patterned and disposed over the substrate, theorganic EL material may be disposed over the patterned first electrode,and the second electrode may be disposed over the organic EL material,the first device may further include a bus line disposed over thesubstrate. The patterned first electrode of each of the plurality ofOLED circuit elements may be electrically connected to the bus linethrough at least one fuse. An example of such embodiments is shown inFIG. 7 and described herein. In some embodiments, the patterned firstelectrode of each of the plurality of OLED circuit elements may befabricated in a single step with the fuses (such as through lithographyor deposition steps), which may decrease fabrication time and costs. Insome embodiments, the fuse and the first electrode may comprise the samematerial.

The reference to a “single step” above, and as would be appreciated byone of ordinary skill in the art, refers to performing the fabricationof the fuse and the electrode simultaneously. That is, each componentmay be fabricated simultaneously, even if there are multiple processesinvolved in the fabrication. For example, the process of patterning theelectrodes and the fuses may include both photolithography and chemicaletching processes. However, these processes may be performedsimultaneously in what may be considered essentially the samefabrication step because, for instance, the components may be patternedfrom the same layer of conductive material that was deposited on asubstrate. As described below, the fabrication of the fuse and theelectrode simultaneously may provide some increased efficiencies,freedom of design (particularly with regard to the fuse design), and/orreduce manufacturing costs.

An insulating layer may be disposed between each of the fuses and theorganic EL material in some embodiments. This insulating layer may serveto protect the EL material from damage when a fuse is opened due to anexcess current, such as, for instance, when there is a short circuit inthe OLED circuit element. In some embodiments, the insulating layer maybe disposed over the fuses, and the organic EL material may be disposedover the insulating layer. In some embodiments, the insulating layer mayform a grid layer over the substrate. The grid layer may define theemissive area of each pixel. For instance, the grid layer may comprise alayer of insulating material that is disposed in the area of the devicearound (i.e. over) the fuses and in-between the first electrodes of theOLED circuit elements in the first device. In some embodiments, theplurality of OLED circuit elements may be disposed on the substrate inthe same plane as the bus line. For instance, the bus line may not bedisposed over the OLED circuit element, and the OLED circuit element maynot be disposed over the bus line.

The fuses may connect the first electrode of each OLED circuit elementto the bus line in some embodiments. Generally, fuse materials used insuch embodiments may comprise TCOs, such as ITO or IZO. Thecross-sectional area of the fuse may typically be designed so as to belarge enough to ensure sufficiently high conductivity, yet small enoughto ensure sufficiently high transparency (such that the fuses do notsignificantly impede the light emitted from the device). In someembodiments, where the fuse and electrode are patterned from the samematerial, at substantially the same time, and/or to substantially thesame thickness, some properties of the fuse may be determined byparameters preferred for the electrode performance. For example, whereit is desired that the electrode is transparent, the fuse material andthickness may be selected with this criteria in mind. Other fuseparameters (such as the width of the fuse) may also be used to ensurethat the fuse functions as a fuse (that is, so that the fuse opens theelectrical connection in response to an excess current). The inventorshave found that a preferred range of the thickness of the fuse in someembodiments may be between approximately 30 nm and 300 nm.

In addition to the thickness of the fuse, the ratio of the length of thefuse to the width of the fuse in some embodiments (where the width ofthe fuse, as illustrated by fuse shown in FIG. 8, is the dimension ofthe cross-sectional area that is not the thickness) may preferably below enough such that the fuse is conductive under normal operation (i.e.the length divided by the width is sufficiently low), but be high enoughso as to generate enough heat to burn the fuse upon the occurrence of anexcess current through the fuse (i.e. the length divided by the width issufficiently high). As would be understood by one of ordinary skill inthe art, the fuse may also open an electrical circuit in response to anexcess current in any suitable manner, including ablating, cracking, orany of the other known methods described above. That is, generally thegreater the width of the fuse, the less resistance the component willhave and the greater the current needed to open the fuse. In contrast,generally the longer the length of the fuse, the greater the resistanceand thereby the less current that may be needed to open the fuse. Theinventors have found in this regard that a preferred range for the fusesis to have a length-to-width ratio between 0.1 and 5.0. However, anylength to width ratio that enables the fuse to open an electricalconnection in response to an excess current, such as when a shortcircuit occurs (or begins to occur), is contemplated as within theseembodiments.

The bus line may, in some embodiments, be an integrated bus line suchthat a single bus line electrically connects to the first electrode ofeach of the plurality of OLED circuit elements through a fuse. In someembodiments, the bus line may comprise a plurality of segmented buslines.

In some embodiments, in the first device as described above, where thesecond electrode may be disposed over the substrate, the organic ELmaterial may be disposed over the second electrode, and the firstelectrode may be patterned and disposed over the organic EL material,the first device may further include an integrated bus line. Theintegrated bus line may electrically connect each of the plurality ofOLED circuit elements together. Preferably, the integrated bus line maybe disposed in the area of the first device between the first electrodeof each of the plurality of OLED circuit elements. As used in thiscontext, “between” may refer to when at least a portion of the bus lineis in the plane of the first electrode of the plurality of OLED circuitelements and the bus line thereby separates the first electrodes. Anexample of such embodiments is shown in FIGS. 12(a)-(d) and describedbelow. However, in some instances, a portion of the bus line may extendover the first electrode of an OLED circuit element. In someembodiments, the integrated bus line may be disposed over the firstelectrode of the plurality of OLED circuit element. The first electrodeof each OLED circuit element may directly connect to the integrated busline, or may electrically connect to the bus line though another circuitcomponent.

In some embodiments, the first electrode of each of the plurality ofOLED circuit elements may be the fuse. Thus, it may be preferable thatthe first electrode of each of the OLED circuit elements may have athickness such that it is ablated in response to an excess current. Thethickness of the fuse in some such embodiments may be the dimension ofthe fuse that is disposed substantially along the axis that isperpendicular to the plane of the substrate.

A first method for fabricating an OLED with a short tolerant structuremay also be provided. The first method may include obtaining (orproviding) a substrate having a first electrode. As used in thiscontext, “obtaining” may comprise, for example, depositing a layer ofconductive material on a substrate, wherein the layer of conductivematerial will form, at least in part, a first electrode on an OLEDcircuit element. In some embodiments, “obtaining a substrate having afirst electrode” may also comprise receiving a substrate that alreadycomprises a layer of conductive material disposed thereon. In general,any method of obtaining or providing a substrate is contemplated to bewithin the scope of this embodiment.

The first method may further include depositing an organic EL materialover the first electrode. Any suitable method of depositing EL material,including those discussed above, may be utilized as would be understoodby one of ordinary skill in the art.

The first method may further include depositing a plurality ofphysically segmented second electrodes over the organic EL material. Thestep of depositing the segmented second electrodes may include anymethod for depositing a patterned layer in an OLED, including thosediscussed above, such as by way of example only, deposition through amask, cold welding, and/or patterning associated with some of thedeposition methods such as ink jet and OVJP. Other methods may also beused, as would be understood by one of ordinary skill in the art.

The first method may further include, in some embodiments, the step ofdepositing an insulating material over the physically segmented secondelectrodes, such that a portion of each of the second electrodes remainsexposed through the insulating material. The first method may includedepositing an unpatterned blanket layer of a conductive material suchthat the blanket layer of conductive material electrically connects tothe portion of each of the second electrodes that remains exposedthrough the insulating material. The electrical connections between theunpatterned blanket layer of conductive material and the exposed portionof each of the plurality of second electrodes may form a fuse (such asin the embodiment shown in FIGS. 6(a)-(d)). In this manner, the fuse maycomprise a portion of the unpatterned blanket layer. For instance, thefuse and the unpatterned blanket layer may comprise the same materialand/or be deposited in the same process. This may reduce the number offabrication steps and thereby reduce manufacturing costs. This may alsoincrease reliability and/or decrease manufacturing error because anelectrical connection between the first electrode and the top conductivelayer may be more readily obtained. However, embodiments are not solimited, and in some embodiments, the fuse may comprise a differentmaterial from the unpatterned blanket layer. Further, in someembodiments, the fuse may be deposited in a separate process from thedeposition of the unpatterned blanket layer.

A second method for fabricating an OLED with a short tolerant structureis also provided. The second method may include obtaining or providing asubstrate having a first conductive layer disposed thereon. As notedabove, “obtaining a substrate” may comprise, for example, depositing alayer of conductive material on a substrate. In some embodiments,obtaining a substrate having a first conductive layer may comprisereceiving a substrate that already comprises a layer of conductivematerial disposed thereon. However, any method of obtaining a substrateis contemplated to be within the scope of this embodiment. Preferably,the first conductive layer comprises a TCO such as ITO or IZO (which isoften considered a suitable alternative material to ITO for manyapplications).

In some embodiments, the second method may further comprise defining aplurality of physically segmented first electrodes on the firstconductive layer. The first electrodes may be defined such that they arenot electrically connected in series. A plurality of fuses may also bedefined on the first conductive layer. In some embodiments, the firstelectrode and the fuses may be defined at the same time, therebydecreasing the number of steps performed in the manufacturing processes.The first electrode and the fuses may be defined by, for instance, usingphotolithography. However, any suitable method for defining the fusesand the first electrodes may be used, as would be understood by one ofordinary skill in the art. For example, the step of defining (e.g.patterning) the first electrode and the fuse may includephotolithography followed by wet or dry etching, where the fuse andelectrode are each defined simultaneously. In some embodiments, thefirst electrodes may comprise the anodes of a pixel of each of aplurality of OLED circuit elements that comprise a device.

The second method may further include fabricating a bus line over thesubstrate. This fabrication step may include, in some embodiments,depositing a conductive material onto the substrate. The bus line maycomprise a highly conductive material. In some embodiments, the bus linemay be an integrated bus line or it may comprise a plurality ofsegmented bus lines. In some embodiments, each of the plurality ofsegmented (e.g. patterned) first electrodes may be electricallyconnected to the bus line through at least one fuse. In this manner, ifexcess current arising from a short circuit (or any other source) beginsto flow through the segmented first electrode, the first electrode maybe electrically isolated from the rest of the components of the deviceby the fuse (i.e. the fuse may open an electrical connection and therebyelectrically isolate the short). In some embodiments, the fuses may beconfigured so as to ablate in response to an excess current. Forinstance, the fuses may have a thickness such that at normal operation(i.e. normal operational current levels), the fuse conducts currentbetween the bus line and the first electrode; however, when excesscurrent is provided (e.g. based on a short), the current ablates thefuse.

That is, for example, if excess current arising from a short circuit (orany other source) begins to flow through a segment of the firstelectrode (i.e. the first electrode of one of the pixels), the segmentedfirst electrode of that pixel may be electrically isolated from the restof the components of the device (e.g. the other pixels) by the fuse(i.e. the fuse may open an electrical connection and therebyelectrically isolate the short). In some embodiments, the fuses may beconfigured so as to ablate, crack, or open the electrical circuitthrough any other chemical or physical process in response to an excesscurrent.

Continuing with the second method as described above, the second methodmay include step of depositing organic EL material over the firstelectrodes (preferably after the bus line is fabricated over thesubstrate). In general, the step of depositing the organic EL materialmay be performed after the bus line is fabricated so as to decrease thelikelihood of damage to the more sensitive organic material during thefabrication of the bus line. The second method may further includedepositing a second electrode over the organic EL material. The secondelectrode may comprise a blanket layer such that a plurality of OLEDcircuit elements shares a common second electrode. However, embodimentsare not so limited, and therefore in some embodiments, the secondelectrode may be deposited as a patterned layer.

According to some embodiments, the second method of fabricating an OLEDcomprising a short tolerant structure may include the step of depositingan insulting layer over the fuses. It may be preferred, in someembodiments, that the insulating layer may be disposed so that the ELmaterial is not damaged when a fuse opens an electrical connection. Theinsulating layer may be deposited over the bus line and/or in the areaof the device in-between the pixels of the OLED circuit elements so asto form a grid layer that defines the emissive pixel areas.

In some embodiments, a first device may be provided. The first devicemay include a substrate and a plurality of OLED circuit elementsdisposed on the substrate. Each of the OLED circuit elements may includeone, and only one, pixel. As noted above, the OLED circuit element mayinclude other circuit components as well. Each OLED circuit element mayinclude a fuse adapted to open an electrical connection in response toexcess current in the pixel. For example, the fuse may open a circuit ifa short begins to develop in or near the pixel. The OLED circuitelements may include more than one fuse, such as when a plurality offuses is electrically connected in parallel. Each pixel may include afirst electrode, a second electrode, and an organic electroluminescent(EL) material disposed between the first and the second electrodes. Insome embodiments, each of the OLED circuit elements may not beelectrically connected in series with any other of the OLED circuitelements.

In some embodiments, in the first device as described above, theplurality of OLED circuit elements may be commonly addressable. Suchembodiments may, for instance, correspond to a lighting device in whichthere may be no need or requirement that each of the OLED circuitelements be individually addressable (which may typically be the casefor a display such as an AMOLED or PMOLED). That is, in someapplications, for example where the first device may comprise a lightingpanel, the functionality of the first device may be such that each ofthe OLED circuit elements may be electrically connected so that eachpixel is illuminated (or not illuminated) at the same time. This may bepreferred so as to reduce the fabrication costs associated with thecircuitry and control units that may otherwise be required foraddressing each pixel individually (or a group of pixels). Previously,when designing lighting panels, it was generally the case that it wasdesirable that such devices comprise as few separate OLED pixels aspossible because defining each pixel (including electrical connectionsas needed) would increase costs and/or affect the uniformity of thedevice. However, as noted above, the inventors have found that in someembodiments by increasing the number of pixels, and electricallyconnecting the pixels in parallel, if an excess current were to occur inone or more of the pixels, the effect could be minimized by the fusescorresponding to each pixel so as to not appreciably alter the overallperformance of the device. Moreover, unlike a display such as an AMOLEDor PMOLED, the number of pixels in such embodiments may not be dictatedby the desired resolution of the device. That is, for instance, thenumber of pixels in a display is typically based on the resolution ofthe display and is thereby pre-determined. In some embodiments ofdevices provided herein, the device may comprise any number of pixelsand in any configuration so as to minimize the effect of a short in oneor more pixels, while keeping fabrication costs within a tolerable limitand providing more design freedom.

It should be noted that embodiments are not so limited to commonlyaddressable embodiments, and in some instances, one or more of the OLEDcircuit elements may be separately addressable from one or more of theother OLED circuit elements.

In some embodiments, in the first device as described above, the fusemay comprise substantially the same material as the first electrode. By“substantially the same” it is generally meant that the fuse and thefirst electrode may comprise the same concentration materials and/orcombinations of materials, within experimental or manufacturing error(e.g. within 5% of the amount and/or concentration of materials). Insome embodiments, the fuse may comprise the same material as the firstelectrode.

Such embodiments may provide the advantage that the first electrode andthe fuse may be fabricated in the same step (e.g. deposited at the sametime or defined during the same process from the same layer of depositedmaterial), thereby reducing the costs and complexity of manufacturing.Moreover, the inventors have found that utilizing the same or similarmaterial as the first electrode for the fuse (rather than, for instance,using the same or similar material as the bus line) may be advantageousin some instances because the electrode may comprise a more resistive(e.g. less conductive) material than the bus line. Examples of suchmaterials may include transparent conductive oxides (TCO), such as ITOor IZO. This may permit the fuse to have a larger thickness (e.g. on theorder of approximately 100 nm), while still providing the desiredfunctionality of opening an electrical connection when an excess currentis conducted through the pixel. In general, the larger the dimensions ofa component, the more efficiently and accurately it may be fabricated.In contrast, the bus line of some devices may comprise a more conductivematerial (e.g. Aluminum, Copper, Gold, or Silver), particularly inembodiments where there may be a large number of pixels connected inparallel (which may more conductive bus line to carry a large amount ofcurrent with less resistive power loss). If a fuse was to comprise thesame material as the bus line in such embodiments, the fuse would likelyrequire a relatively small thickness (and/or width) so that it wouldstill function properly as a fuse for typical currents of an OLED. As anexample, in a typical lighting panel, a fuse that comprises Aluminum mayrequire a thickness that is less than or equally to 10 nm. Fuses havingsuch small dimensions for a thickness may be more difficult toaccurately and efficiently fabricate, and may thereby increase the costsand/or manufacturing failures of such devices. The more conductivematerials may also be less transparent than TCO materials, and maythereby block portions of the light emitting area of the device, whichmay limit the type of OLED that may be fabricated.

Moreover, in general, it may be desirable to utilize a bus line that hasa high conductivity to reduce resistive loses and maintain a uniformvoltage across the panel (at least as uniform as may be achieved). Thus,by forming the fuse and/or electrode of a different material than thebus line, embodiments may provide for greater design freedom, includingthe potential choice of components for the bus line that may take intoconsideration factors such as costs, uniformity of the panel,transparency, etc., without the further constraint of choosing amaterial such that the fuses will operate at a desired current.

In some embodiments, in the first device as described above, the fuseand the first electrode may each have a thickness and the thickness ofthe fuse and the thickness of the first electrode may be approximatelythe same. By “approximately the same,” it is generally meant that thethickness of the fuse and the electrode may be within 10% of oneanother. In this context, the “thickness” of the fuse and the thicknessof the first electrode may refer to the dimension of the fuse and theelectrode that is substantially perpendicular to the plane of thesubstrate. Thus, the thickness may, in some instances, be the result ofthe amount of material deposited during a single deposition step. Insome embodiments, the fuse may have approximately the same thickness andcomprise the same (or substantially the same) material as the firstelectrode. The fuse and the electrode may thereby be fabricated during,for instance, the same deposition step or may be formed from the samelayer of deposited material (e.g. using photolithography, which may befollowed by wet or dry etching). As noted above, this may reduce thenumber of fabrication steps, including the requirement to accuratelyalign a plurality of deposition masks during manufacturing of each ofthese components.

In some embodiments, in the first device as described above, the firstelectrode may be patterned, the first electrode may be disposed over thesubstrate, the organic EL material may be disposed over the firstelectrode, the second electrode may be disposed over the organic ELmaterial, a bus line may be disposed over the substrate, and the firstelectrode of each of the plurality of OLED circuit elements may beelectrically connected to the bus line through the fuse. An example ofsuch a layout is shown in FIGS. 7(a) and (b); however, embodiments arenot so limited. In some embodiments, the fuse and the first electrodemay each have a thickness and the thickness of the fuse and thethickness of the first electrode may be approximately the same. As notedabove, such embodiments where the thicknesses of the fuse and the firstelectrode are substantially the same may enable each component to befabricated in the same step (such as during the same deposition ofmaterials or defined from the same layer of previously depositedmaterial). It should be noted that, in general, if the fuse and thefirst electrode have approximately the same thickness and comprise thesubstantially same material, than the fuse will likely be designed tohave a different (and smaller) width than the first electrode such thatthe fuse will have a higher resistance than the electrode when the samecurrent flows through each component, and thereby the fuse will open thecircuit in response to an excess current. In some embodiments, the busline may also have a thickness such that the thickness of the fuse andthe thickness of the bus line may be different. That is, for instance,the bus line may have a thickness that is independent of the fuse, whichmay enable each of these components to be designed so as to maximize itsfunctionality (e.g. the bus line may be chosen so as to have a thicknessand material to effectively conduct electricity with low resistive powerlosses, while the fuse may be chosen so as to open an electrical circuitin response to an excess current and have other properties that may bedesirable such as transparency).

In this regard, in some embodiments of the first device comprising a busline that is connected to each pixel via a fuse, the fuse may comprisesubstantially the same material as the first electrode and/or the fusemay comprise a different material than the bus line. In someembodiments, the fuse may comprise a transparent conductive oxide, suchas ITO or IZO.

In some embodiments, in the first device as described above, the fuseand the first electrode are integrally coupled. As used in this context,“integrally coupled” may refer to when the fuse and the first electrodeare fabricated in the same manufacturing step and may comprise the samematerial such that the fuse may be viewed as a component of theelectrode (but may have a different dimension, such as its width). Inthis regard, the fuse itself may not comprise a “separate” component,but may be a continuous extension of the first electrode; however, thefuse may be designed such that as an excess current begins to flowthrough the first electrode, the fuse opens the electrical circuit.

The inventors have also found that it may be beneficial in someembodiments to electrically connect each of the OLED circuit elements toa plurality of fuses, where each fuse is electrically connected inparallel. For example, in the first exemplary device as describedcomprising a bus line, each pixel may be electrically connected to thebus line via two or more fuses. Replacing a single fuse with multiplesmaller fuses may provide several advantages. First, it may provide moretolerance in design and manufacturing process. Second, multiple smallerfuses may help to distribute heat so there is no concentrated heat inone spot. Third, multiple fuses provide redundancy so even if one fuseis not functional (e.g. due to defects or particles) the rest of fusesstill keep the pixel working. Moreover, by controlling the width of thefuses, embodiments may enable the thickness of the fuses to correspondto, for instance, the thickness of the first electrode such that eachmay be fabricated in a single step.

Reference will now be made to the remaining figures to illustrateseveral embodiments. These embodiments are designed to be exemplary, andare not to be construed as limiting or as an exhaustive list. Thefigures and discussions presented below focus on several configurationsof segmented electrodes and fuses, and thereby may omit other portionsor details of the OLED device for simplicity.

FIGS. 4(a)-(d) show an exemplary embodiment of the first device thatcomprises a plurality of patterned thin conductive first electrodes 401and segmented highly conductive bus lines 402. In particular, FIG. 4 (a)shows the exemplary embodiment of the first device in normal operation;FIG. 4 (b) shows the cross-sectional view of this exemplary embodimentin normal operation; FIG. 4 (c) shows the same exemplary embodiment ofthe first device after a fault has occurred; and FIG. 4 (d) shows thecross-sectional view of this exemplary embodiment after a fault hasoccurred.

Although the referred to as a “thin conductive first electrode,” aswould be understood by one of ordinary skill in the art, the actualthickness of the first electrode may depend on a variety of factors,including, by way of example, the material of the first electrode (e.g.its conductivity) and the current at which the first electrode may actas a fuse so as to open an electrical connection.

With particular reference to FIGS. 4 (b) and (d), this exemplaryembodiment comprises a plurality of OLED circuit elements each having apixel 400, where each pixel has a second electrode 404 disposed over asubstrate 403; an organic EL material 405 disposed over the secondelectrode 404; and a first electrode 401 that is patterned and isdisposed over the organic EL material 405. A plurality of segmented buslines 402 electrically connects the patterned first electrode 401 ofeach of the plurality of OLED circuit elements together. As shown inFIGS. 4(a)-(d), the plurality of segmented bus lines 402 are disposedover the first electrodes 401. In some embodiments, the segmented buslines 402 may be disposed in other locations, including over, under, orbetween the first electrodes 401 of each of the OLED circuit element.According to the exemplary embodiment shown in FIGS. 4(a)-(d), the firstelectrode 401 of each pixel 400 of the plurality of OLED circuitelements is a fuse. That is, the first electrode 401 has a thicknesssuch that, in response to an excess current, the first electrode 401 maybe ablated (or otherwise open the electrical connection). In thisexemplary embodiment, the thickness of the first electrode 401 refers tothe dimension of the first electrode 401 that is disposed substantiallyalong the axis that is perpendicular to the plane of the substrate 403.

In some embodiments, where the first electrode 401 comprises the fuse,the inventors have found that an acceptable range for the thickness ofthe first electrode 401 to operate effectively as a fuse may be betweenapproximately 1 nm and 60 nm for fuses comprising aluminum (or any othersuitable material, such as Mg:Ag) in some commercial devices. Thisrelatively low thickness may be used in some embodiments because theelectrode material may typically comprise a high conductivity metal,such as aluminum, which is designed to ablate (or otherwise open theelectrical connection) in response to an excess current (such as when ashort circuit begins to form). As another example, for a first electrodecomprising indium tin oxide (ITO) and having dimensions 30 μm×30 μm, ina device designed to have a melting current for the fuse of 30 mA, athickness for the first electrode so that is functions properly as afuse at 30 mA was found to be approximately 120 nm. However, as notedabove, any thickness or material may be used based on the desiredproperties of the device, as would be understood by one of ordinaryskill in the art. For example, a fuse could be fabricated, tested for amelting current by determining the current at which it ablates (orotherwise opens an electrical connection), and then the parameters couldbe adjusted (e.g. dimensions or materials) to obtain a desiredfunctionality (i.e. melting current), as was described above.

FIG. 4 (a) shows a top view of the first device according to thisexemplary embodiment in normal operation. During normal operation, thecurrent through the first device is approximately equally divided by thetotal number of rows (n_(row)) shown in FIG. 4 (a). Therefore, themaximum current in each row is approximately I_(on)=I_(o)/n_(row), whereI_(o) is the total current flowing through the device. In the exampleshown in FIG. 4, there are 5 rows, so ideally (i.e. without consideringimperfections of the device) I_(on)=I_(o)/5. This is the maximum currentthrough the first electrode 401 at normal operation.

FIGS. 4 (c) and (d) show the first device after the occurrence of ashort fault (or other excess current). When a pixel 400 is shorted,nearly all the current I_(off)=I_(o) will flow through this pixel 400 atthe location of the short (or there will be a significant increase inthe current). According to this exemplary embodiment, the firstelectrode 401 of each of the plurality of OLED circuit elements has athickness such that when a large current flows through a shorted firstelectrode 406, the shorted first electrode 406 will heat up and beablated from the organic layer 405, thereby acting as a fuse to open theelectrical connection. When the first electrode of one of the OLEDcircuit elements is ablated, there is no longer an electrical connectionbetween the shorted first electrode 406 and the segmented bus lines 407that had been in electrical contact with the electrode. Therefore, theablation of the first electrode transforms the short fault into an openfault, preventing any current from flowing through the shorted pixel.Furthermore, in the embodiment illustrated in FIG. 4, segmented buslines 407 that had been connected to the first electrode 406 that wasablated are also electrically isolated, and thereby no current flowsthrough these components either.

The ratio of short circuit current to the current during normaloperation defines the sensitivity “S.” This ratio indicates thetolerance that may be used in the fuse design and dictates the maximumfluctuation the fuse may experience before opening the electricalconnection. For this exemplary embodiment shown in FIGS. 4(a)-(d), thesensitivity is:S=I _(off) /I _(on) =n _(row)

Embodiments similar to the one depicted in FIGS. 4(a)-(d) that comprisesegmented bus lines and/or where the first electrode of each OLEDcircuit element comprises a fuse may have the additional benefit ofbeing fault tolerant in relation to shorts that may occur in other partsof the device, such as the bus lines. For instance, if a bus line 407 isshorted, the excess current that flows through that short may passthrough the first electrode of only two OLED circuit elements. Bychoosing a thickness of the first electrodes 401 so that it ablates whenI_(off)=I₀/2, the device may be tolerant to these faults as well. Thatis, if such a fault occurs, the fuses (i.e. the first electrodes 401)may ablate and thereby electrically isolate the shorted segmented busline.

FIGS. 5(a)-(d) show an exemplary embodiment of the first device thatcomprises islands of thick conductors 501 (e.g. segmented electrodes)further having a thin layer of conductor 502 and 506 disposed over thethick conductors 501, where the portions of the thin conductor 506 atthe interconnects between the thick conductors are fuses. Morespecifically, FIG. 5(a) shows an embodiment of the first device innormal operation; FIG. 5(b) shows the cross-sectional view of thisexemplary embodiment in normal operation; FIG. 5(c) shows the sameembodiment of the first device after a fault has occurred; and finallyFIG. 5(d) shows the cross-sectional view of this exemplary embodimentafter a fault has occurred.

As was noted above, although reference may be made to a “thick” layer ofconductive material (i.e. the electrode) and a “thin” layer ofconductive material, the actual thickness of each of these components(and, correspondingly, the relative thickness of the two layers ofconductive material) may depend on a variety of factors, including thematerial used for each layer. For example, in some embodiments the“thick” and the “thin” conductive layers may have approximately the samethickness (or the “thin” layer may even have a greater thickness thanthe “thick” layer), but the “thin” layer of conductive material maycomprise a material that has a higher resistivity than the “thick” layerof conductive material. In other embodiments the “thick” and the “thin”conductive layers may have approximately the same thickness (or the“thin” layer may even have a greater thickness than the “thick” layer),but the “thin” layer of conductive material may comprise a material thathas a lower melting temperature than the “thick” layer of conductivematerial. Thus, in the embodiments described below, reference could alsobe made to a “first” layer (in place of a “thick” layer) of conductivematerial and a “second” layer (in place of a “thin” layer) of conductivematerial to describe the exemplary structures. However, for illustrationpurposes only, reference may be made generally to a “thick” and a “thin”layer.

In addition, although an electrode (or electrodes) may be referred to asan “island,” this does not require that each of these electrodes must bephysically isolated from the other components of the device. Forinstance, each of the conductive “islands” may be connected to othercomponents (including the electrode of one or more of the other pixels)by a component or components (such as a fuse), as would be understood byone of ordinary skill in the art. Thus, the reference to an “island” issimply intended to illustrate that each of these components comprises aphysically separate component from one another (e.g. each island mayform the electrode of one pixel). Each of these electrodes may beelectrically isolated from each of the other electrodes if a shortoccurs in the pixel of that electrode by a fuse.

The exemplary embodiment depicted in FIGS. 5(a)-(d) comprises a secondelectrode 504 disposed over a substrate 503, an organic EL material 505disposed over the second electrode 504, a first electrode 501 that ispatterned and is disposed over the organic EL material 505, and a thinlayer of conductive material 502 and 506 that electrically connects thepatterned first electrode 501 of each pixel together. The patternedfirst electrode 501 of each pixel 500 may be a thick layer of conductivematerial. In this exemplary embodiment, the thickness of the thick 501and the thin 506 conductive layers is the dimension of the layer that isdisposed substantially along the axis that is perpendicular to the planeof the substrate 503. In some embodiments, the inventors have found thatit may be preferred that the thick layer of conductive material 501 mayhave a thickness between approximately 10 nm and 500 nm and the thinlayer of conductive material 502 and 506 may have a thickness betweenapproximately 1 nm and 60 nm. However, in some embodiments, theinventors have found that the thick layer of conductive material 501 mayhave a thickness between approximately κ nm and 1 um and still functionfor its intended purpose. In some embodiments, it may be preferred, aswas described above, that the thick layer of conductive material 501 hasa thickness that is at least twice as great as the thin layer ofconductive material 506.

As depicted in FIG. 5 (a), the thin conductive layer may be unpatterned,and may comprise a portion 502 of a conducting layer that is disposedover the patterned first electrode 501 of each of the pixels 500, and aportion 506 that is disposed over an area of the first device that isbetween the OLED circuit elements. This portion of the thin layer ofconductive material 506 that is disposed over the area between the OLEDcircuit elements may have properties such that it functions as a fuse.For instance, and as shown in FIGS. 5(c) and (d), this portion of thethin conductive layer 506 may have a thickness such that it ablates inresponse to an excess current, such as when a short circuit occurs. Whenexcess current flows through the first electrode 501, the interconnectregion 506 around the first electrode 501 may be ablated, therebycreating an open circuit 507 that electrically isolates the OLED circuitelement where the short occurred. In some embodiments, it may bepreferred that each of the OLED circuit elements comprises the thicklayer of conductive material 501 and at least a portion of the thinlayer of conductive material 502.

One example of a method to fabricate a device according to thisexemplary embodiment may be to deposit the thick conductive islands 501(preferably Al) followed by a thin blanket conductive layer 502 and 506,as shown in FIG. 5(b). In the normal operation mode, the thin conductivelayer 502 and 506 will conduct the current from one conductive aluminumisland 501 (i.e. the first electrode) to the next. However, when apotential short occurs, the current may be large enough that it willheat up the thin blanket layer at the inter-connect regions 506 so thatthese portions are ablated and thereby create an open circuit 507, asshown in FIGS. 5(c) and (d). Thus, the portion of the blanket layer thatforms the interconnects 506 between the first electrode 501 of thepixels may comprise a fuse in this embodiment.

In some embodiments, instead of a blanket layer of thin conductivematerial, the thin layer of conductive material may be patterned to formthe interconnects 506 between the first electrode 501 of the OLEDcircuit elements. In this embodiment, the thin conductive layer may notbe disposed over any portion of the patterned first electrode 501 of thepixels 500, or may be disposed over only a portion thereof.

In the exemplary embodiment shown in FIGS. 5(a)-(d), the maximum currentduring normal operation in each row for this embodiment may be the sameas in the first exemplary configuration: approximatelyI_(on)=I₀/n_(row). However, because there are potentially as many asfour fuses for each island of thick conductive material 501(corresponding to the interconnect regions 507 between each firstelectrode 501), any excess current, such as a short circuit current,will be shared by as many as four connections 506 (this may be the worstcase scenario because current may prefer one path rather than theothers). Although some of the first electrodes 501 may have less thanfour interconnections based on their location within the first device,the first electrode 501 of many of the pixels 500 in these embodimentsmay have at least four interconnects 506. At each of these connections(i.e. the fuse) 506, the short circuit current may be approximatelyI_(off)=I₀/4. The sensitivity in this case can be calculated by:S=I _(off) /I _(on) −n _(row)/4.

Some of the potential advantages of the first and second exemplaryembodiments may include: (1) the embodiments may function properlyirrespective of the location of the short in the device. That is, if ashort occurs either under the patterned first electrode or occurs at theinter-connect between the first electrode of a plurality of OLED circuitelements, the proper fuse (or fuses) will burn (or otherwise open) andthus protect the rest of the area of the first device; and (2) the fusesmay be disposed over the pixels, so any by-products generated from theburnt/ablated (or otherwise opened) fuse will remain outside of theOLEDs. It should be understood that this is not an exhaustive list ofthe benefits of these two embodiments. Some of the potentialdisadvantages of the first two exemplary embodiments may include: (1)the embodiments may create more resistive power losses due to Ohm's law(i.e. I (current)×R (resistance)) due to the higher resistance of thecathode based on the patterned first electrodes of the pixels, as wellas the resistance of the fuses and the interconnects; (2) thesensitivity is relatively low when there is a small number of rows; and(3) a shadow mask may be required to deposit and pattern the firstelectrodes of the cathode; however, patterning the cathode through useof the shadow mask may lose the fill factor.

Another potential advantage that some of these embodiments may offer isthat the resistance of the anode or cathode may be controlled based, atleast in part, on the segmented first electrodes and the interconnectsbetween them. This may make the panel more uniform because the cathodepotential may be controlled to compensate for potential drops across theanode or vice-versa. When balanced, this may result in a more uniformpotential on the OLEDs across the whole first device.

In general, when potential drops across the anode and cathode of adevice are different, or when the potential drops in delivering chargefrom the power source to the anode and cathode of a device aredifferent, it may result in a non-uniform current flow through thedevice and the device may emit light unevenly. That is, some portions ofthe device may emit more light than other portions. In somecircumstances, it may be desirable to have a device that has an anodeand a cathode with substantially the same sheet resistance, even if theycomprise different materials with different resistivities. In somecircumstances, it may be desirable to have a device where the potentialdrops in delivering charge from the power source to the anode andcathode of a device are substantially the same. This may be achieved byusing the resistance of additional components such as bus lines or fusesto control the potential drops.

In particular, where an anode comprises a first material that has afirst resistivity, and the cathode comprises a second material that hasa second resistivity that is different than the first resistivity,embodiments may provide that additional components may be added,electrically connected, or other modifications may be made to either theanode, the cathode, or both the anode and the cathode such that theirpotential drops may be substantially equivalent. For example, thethicknesses of the anode and cathode layers may be used to control thesheet resistance of each electrode (e.g. if the resistivity of thecathode is twice that of the anode, then if the thickness of the cathodeis also twice that of the anode, then the anode and cathode may have thesame sheet resistance). In other embodiments, if the anode has aninitial sheet resistance that is at least 50% different than the sheetresistance of the cathode, components may be electrically connectedand/or other modifications may be made to either the anode, the cathode,or both so that the potential drops across the anode and cathode or indelivering charge to the anode and cathode are within approximately 10%of each other. In other embodiments, if the anode has an initial sheetresistance that is at least 100% different than the sheet resistance ofthe cathode, components may be electrically connected and/or othermodifications may be made to either the anode, the cathode, or both sothat the potential drops across the anode and cathode or in deliveringcharge to the anode and cathode are within approximately 50% of eachother.

Uniform sheet resistance may be achieved in some instances by decreasingthe equivalent sheet resistance of the anode or cathode that has thehigher initial sheet resistance. For instance, a highly conductivematerial or bus line could be added or electrically connected to themore resistive material so as to match the sheet resistance of the lessresistive material. Other embodiments may achieve this by increasing thesheet resistance of either the anode or cathode that has a lower initialresistivity. For instance, the anode or cathode may be pixilated bysegmenting the material, and interconnects between the segments mayincrease or decrease the overall sheet resistance of the anode orcathode. The “equivalent sheet resistance” may refer to the measure ofthe sheet resistance of the patterned conductive layer integrated withvarious electrical connections. This may include, for example, the sheetresistance of electrodes, bus lines, fuses or any other components.

In this regard, in some embodiments, a device may comprise a firstconductive layer that is patterned to form a plurality of physicallysegmented electrodes. The device may also comprise a second electrodethat may, for instance, be common to a plurality of pixels. Thepatterned first electrodes may be electrically connected using anysuitable electronic components including, by way of example, the use ofone or more fuses and/or bus lines. In this manner, the plurality ofpatterned first electrodes that comprise the first conductive layer willhave a first equivalent sheet resistance that is based, at least inpart, on the material that comprises the first conductive layer, thedimensions of the pixilated electrodes, as well as the variouselectrical connections made between the electrodes of each pixel.Similarly, the second conductive layer may have a second equivalentsheet resistance that may be based on, for example, the material thatcomprises the second conductive layer, the dimensions of the secondconductive layer, the electrical components (such as any bus lines)connected to the second conductive layer or portions thereof, and anyother relevant factor. The various factors that determine the equivalentsheet resistance of the first conductive layer and/or the secondconductive layer may be chosen such that first equivalent sheetresistance and the second equivalent sheet resistance may be withinapproximately 50% or more preferably within 10%. In this manner, thefirst device may be designed to emit a more uniform amount of lightacross the device. In some embodiments, the first equivalent sheetresistance and the second equivalent sheet resistance may beapproximately equal. In some embodiments, the first conductive layer maycomprise a material having a first resistivity and the second conductivelayer may comprise a material having a second resistivity, where thefirst resistivity and the second resistivity are more than 10%different. In some embodiments, the difference between the firstresistivity and the second resistivity may be at least 20%, 50%, or100%. That is, for instance, the materials that comprise the firstconductive layer and the second conductive may have substantiallydifferent resistivities. However, by choosing a the other parameters ofthe first conductive layer (such as a particular pixel configurationand/or size), as well selecting the electrical connections and/orcomponents between each of the pixilated electrodes, the equivalentsheet resistance of the first conductive layer that comprises theplurality of first electrodes may be adjusted to compensate for thedifference in resistivity between the first and second conductive layersand thereby achieve a more uniform appearance for the lighting device.

FIGS. 6(a) and (b) show an embodiment of the first device that includesan insulator 602 and a top conductive layer 606. In some of theseembodiments, the conductive island (i.e. the patterned first electrode)601 is electrically isolated from a top conductive layer 606 except fora small portion 607. This small portion 607, which forms the electricalconnection between the patterned first electrode 601 of the pixel 600and the top conductive layer 606, may comprise the fuse.

More specifically, this exemplary embodiment shown in FIGS. 6(a) and (b)includes a second electrode 604 disposed over the substrate 603, anorganic EL material 605 disposed over the second electrode 604, a firstelectrode 601 that is patterned and disposed over the organic ELmaterial 605, and further includes a top conductive layer 606 and aninsulating layer 602. The insulating layer 602 is disposed over a partof the first electrode 601 of each of the plurality of OLED circuitelements, and the top conductive layer 606 is disposed over theinsulator 602. The fuse 607 electrically connects the first electrode601 of each of the plurality of OLED circuit elements with the topconductor 606. Preferably, the fuse 607 comprises a part of the topconductive layer 606. The fuse 607 may comprise the same material as thetop conductive layer 606 or they may comprise a different material.

The length of the fuse 607 (in this exemplary embodiment, the length isthe dimension of the fuse that is along the axis that is perpendicularto the substrate 603—i.e. the direction of current flow), may bedetermined in-part by the thickness of the insulating layer 602. It maybe preferred in some embodiments that the thickness of the insulatinglayer 602 is between approximately 50 nm and 5 μm. As described above,the length of the fuse 607 may be one of the properties of the fuse thatdetermines the total resistance of the fuse (and thereby the current atwhich the fuse may open the electrical connection).

In this exemplary embodiment, where the flow of current through the fuse607 is substantially perpendicular to the plane of the substrate 603,the fuse 607 may comprise a material(s) that may be a highly conductivemetal, such as aluminum. This may be due in-part because the fuse 607has an area such that it does not block a substantial amount of theactive area (i.e. the emissive area) of the OLED circuit element andthereby need not be transparent. That is, for instance, because the fuse607 may be made of a highly conductive metal, the cross-sectional areaof the fuse 607 may be much smaller than when a TCO is used, but maystill function as a fuse for a desired melting current. For example, theinventors have found that a 30 mA current may be able to blow out (i.e.open) a fuse comprising ITO with a cross-sectional area of approximately3.6 μm² (30 μm×0.12 μm). In comparison, Vapor Transport Epitaxy (VTE)deposited aluminum may typically have a resistivity approximately 250times less than ITO. If the melting current is the same (i.e. 30 mA) andthe resistance of the fuse is fixed, the cross-sectional area of a fuseof this more conductive material may be reduced to 0.00072 μm² for alength of 50 nm, and 0.072 μm², for a length of 5 μm. Thus, the use ofmore conductive materials may enable the fuse 607 to be smaller, andthereby block less of the light emitted by the device.

In general, the third exemplary embodiment described herein maypotentially provide for greater flexibility in the design of the fusegeometry than that provided in some of the other exemplary embodimentsbecause, in part, there are fewer limitations on the preferred dimensionof the fuse along the axis that is substantially perpendicular to thecurrent flow direction.

In some embodiments, this exemplary embodiment of the first device maypreferably be fabricated in the following way: (1) depositing islands ofconductive materials (i.e. segmented), which constitute the patternedfirst electrode 601; (2) depositing islands of insulating materials 602(i.e. segmented), where the footprint of these insulating materials 602are slightly smaller than that of the conductive islands 601 underneath;and (3) depositing a blanket layer of a top conductive layer 606, whichis disposed across the first device. When the top conductive layer 606is deposited, the conductive material may form electrical connections607 to the conductive islands (i.e. patterned first electrodes) 601,thereby forming a vertical connection 607, as shown in FIG. 6(a). Thisconnection can also be achieved by connecting the edge of the conductiveisland 601 to the top conductor 606.

Under normal operating conditions, a current flows through each pixel600 to the cathode island (i.e. first electrode) of that pixel 601, andcontinues to the top conductive layer 606 through the vertical fuse 607.However, for instance when this pixel 600 is shorted, an excess currentwill cause the vertical fuse 607 to open the electrical connection 608,causing the cathode island 601 to be isolated from the top conductivelayer 606, and thereby the rest of the first device. The sensitivity ofthis embodiment can be calculated as follows:I _(on) =I ₀/(n _(row) *n _(column))I _(off) =I ₀.S=I _(off) /I _(on) =n _(row) *n _(column)

A few of the potential advantages of this exemplary embodiment mayinclude: (1) the top conductive layer 606 may be highly conductive, sothere may be minimum resistance between the first patterned electrodes601; and/or (2) the sensitivity of this embodiment may be very high,which means there is a large tolerance in the fuse design andfabrication. Other advantages of this exemplary embodiment may alsoexist.

A potential disadvantage/challenge of this design is to patterninsulators 602 on top of OLEDs circuit elements, which may increase thecomplexity of the fabrication process. Another potential disadvantagethat was noted with regards to some of the other exemplary embodimentsis that a shadow mask may be used to pattern the layers, which mayreduce the fill factor.

FIG. 7(a) shows a top view of an exemplary embodiment of the firstdevice. In this exemplary embodiment, the fuse 706 is incorporated atthe electrode 701 that is closer to the substrate. In many suchembodiments, this electrode 701 is the anode. This embodiment may permitthe use of a photolithography process to fabricate the fine featuresrequired to realize the fuse structure 706. One example of the layout ofa device implementing this embodiment is shown and described withreference to FIG. 8.

More specifically, and with reference to FIG. 7, in this exemplaryembodiment of the first device the first electrode 701 is patterned andis disposed over the substrate (not shown), the organic EL material isdisposed over the patterned first electrode 701, the second electrode isdisposed over the organic EL material, and the first device furtherincludes a bus line 702 disposed over the substrate. The patterned firstelectrode 701 of each of the plurality of pixels is electricallyconnected to the bus line 702 through at least one of the fuses 706. Thepatterned first electrode 701 of each of the plurality of OLED circuitelements may, in some embodiments, be fabricated in a single step withthe fuses 706. That is, for instance, the patterned first electrode andthe fuse may comprise the same (or substantially the same) materialand/or may comprise the same (or approximately the same) thickness. Asdescribed in more detail above, using the same material for the firstelectrode and the fuse may not only decrease the manufacturing costs,but may also decrease the complexity of the manufacturing processbecause the fuse may have larger dimensions than embodiments where thefuse comprises the same material as the bus line. This may also providea designer with more control of the selection of the attributes (such asdimension, position, and materials) of each component, particularly thebus line, which is generally preferred to reduce resistive power lossesin the device. In addition, an insulating layer (not shown) may bedisposed between each of the fuses 706 and the organic EL material. Insome embodiments, the insulating layer may be disposed over the fuses706, and the organic EL material may be disposed over the insulatinglayer. The insulating layer may prevent, or reduce the likelihood of,the EL material being damaged in the event that an excess current causesone of the fuses 706 to open, such as when a short circuit occurs.

In some embodiments, the insulating layer may form a grid layer over thesubstrate that defines the emissive area of the pixels. The grid layermay comprise a layer of insulating material that is disposed in the areaof the device around (i.e. over) the fuses 706. In some embodiments, theinsulating layer may be disposed over bus lines. Generally, fusematerials used in such embodiments may comprise, by way of example only,TCOs such as ITO or IZO. The cross-sectional area of the fuse 706 may belarge enough to ensure sufficiently high conductivity, yet small enoughto ensure sufficiently high transparency. Where the fuse 706 andelectrode 701 are patterned of the same material, at substantially thesame time, and to substantially the same thickness, some properties ofthe fuse 706 may be determined by parameters preferred for the firstelectrode 701 performance. For example, where it is desired that theelectrode 701 is transparent, the fuse 706 material and thickness may beselected with this criteria in mind, and other fuse parameters such asthe width may be used to ensure that the fuse 706 functions as a fuse(i.e. that it opens the electrical connection in response to a certainamount of current). A preferred range of the thickness of the fuse 706in some embodiments is between approximately 30 nm and 300 nm.

In addition, in some embodiments, the ratio of the length of the fuse tothe width of the fuse (where the width of the fuse is the dimension ofthe cross-sectional area that is not the thickness) may preferably below enough such that the fuse 706 is conductive under normal operation,but is high enough to generate enough heat to burn (i.e. open) the fuse706 upon the occurrence of an excess current. The inventors have foundthat a preferred range for the fuses may be such that thelength-to-width ratio is between approximately 0.1 and 5.0. However, anylength to width ratio that enables the fuse 706 to open an electricalconnection in response to a desired excess current, such as a currentthat occurs in response to a short circuit, is contemplated as withinthis embodiment.

With continued reference to this exemplary embodiment and FIG. 7, amethod to fabricate such a device for a bottom emission OLED with ananode made of a material such as ITO may include the step of definingthe fuse feature 706 and anode pixel electrode 701 on an ITO coatedsubstrate. As described above, the electrode 701 and the fuse 706 may beconsidered “integrally coupled” in such embodiments. A highly conductivemetal bus line 702 may then be fabricated on the same substrate in a waysuch that the active ITO anode is connected to the bus line 702 througha narrow ITO channel, forming a fuse 706 at the pixel level, as shown inFIG. 7(a). Under normal operation, the current will travel across thepanel through bus lines 702, and continue to the pixilated ITO anodeelectrodes: I_(on)=I₀/(n_(row)*n_(column)). When, for instance, an ITOanode 701 is shorted (or an electrical short forms elsewhere in thedevice), the short may draw an excess current of approximately(I_(off)=I₀) from the bus line 702, which will open the fuse, as shownin FIG. 7(b). By electrically isolating the shorted pixel 707, thecurrent flow through the rest of the panel for light emission may besubstantially maintained. The sensitivity of the fuses of thisembodiment can be calculated as follows:I _(on) =I ₀/(n _(row) *n _(column))I _(off) =I ₀.S=I _(off) /I _(on) =n _(row) *n _(column)

As noted above, while embodiments are not so limited, forming the fuseand the electrode of the same material (e.g. during the samemanufacturing step) may provide for the utilization of fuses that havedimensions that are more readily and accurately fabricated, and therebymay be more likely to function as intended when fabricating commercialembodiments of such devices using typical equipment and processes. Asnoted above, if the fuse comprises a highly conductive material such asthose that are generally used for bus lines, the thickness and/or widthof the fuse would likely be required to be small enough such that thefuse will open the circuit in response to an excess current. Theinventors have found that for some embodiments, this may require athickness on the order of 10 nm or less and/or have a relatively largelength-to-width ratio (e.g. on the order of 50:1 in some instances)particularly if the thickness of the fuse is approximately equal to thethickness of the conductive bus line (which may be the case if eachcomponent is manufactured in the same step). However, the exactdimensions of the fuse, as noted above, may be determined based on thespecific application for the device, as well as the materials andcomponents utilized therein.

Some of the potential advantages that embodiments of such devices mayhave include: (1) that such embodiments may offer high sensitivity; (2)that this embodiment may be easy to fabricate; and (3) that someembodiments may achieve higher fill factor through the utilization ofphotolithography or similar process.

Furthermore, some embodiments may have a low resistive loss due to thefact that the fuse in certain embodiments may be very small (e.g. whenthe pixel is also small). For example, a typical OLED white pixel(without outcoupling) may have a luminance of 2160 cd/m² at 4.25 mA/cm²and 4.21 V. When the active pixel (i.e. the emissive area of the pixel)has a surface area of 1 mm², the current through the pixel isapproximately 0.0425 mA. In some embodiments where the fuse may bedesigned into a square shape and a material such as ITO is used with 15Ohm per square sheet resistance, the voltage drop V_(fuse) on this fusecan be calculated as:V _(fuse)=Current(I)*Resistance(R)=4.25×10⁻⁵ A*15 ohm=6.4×10⁻⁴ Volt

Other materials and geometric shapes may be used to construct the fuse.The inventors have found that, when compared to the typical 4.21 V on anOLED, this smaller voltage associated with the fuse may be considerednegligible. With an exemplary 1 cm by 1 cm pixel, the potential drop onthe fuse will be approximately 0.064 V, which is only 1.5% of thevoltage on the OLED.

FIG. 8 shows a representative layout of a WOLED light panel, where thefuses 801, bus line 803, and first patterned electrodes 804 are shown.The inventors have experimented with this particular embodiment of afirst device by fabricating a WOLED lighting panel based on a pixilatedlighting panel layout that incorporated the exemplary fuse designsdescribed above, as shown in FIG. 8. For each fuse 801, the dimension ofthe fuse along the current flowing direction is defined as L, thedimension of the fuse that is not the thickness and is not disposedalong the direction that the current is flowing is defined as W, asshown in the blown-up view of a fuse 802.

In general, there were four different geometry designs of fusescomprising 120 nm-thick ITO (note that the thickness of the fuse in thisembodiment is the dimension of the fuse that is disposed substantiallyperpendicular to the plane of the substrate) that were tested by theinventors. The dimensions and corresponding resistance and estimatedmelting current of which are listed in Table 1:

TABLE 1 Experimental Fuse Design Characteristics L × W (μm × μm)Resistance (ohm) Melting current (mA) 15 × 40 0.375 R_(s) _(—) _(anode)20 15 × 30 0.5 R_(s) _(—) _(anode) 15 15 × 20 0.75 R_(s) _(—) _(anode)10 20 × 25 0.8 R_(s) _(—) _(anode) 15

FIG. 9 shows experimental results of an experimental WOLED panel thatutilizes this exemplary embodiment. FIG. 9(a) shows the microscopicimage of a completed plate with one single pixel shorting 901. The pixel901 is enlarged in FIG. 9(b), which shows both an early-stage short 903and a well developed short 902. The opened fuse 904 is clearly shown inFIG. 9(c). FIG. 9(d) shows a magnified image of the early-stage short903 and well-developed short 902. Based on factors such as the size andshape of the shorting spot, it can further be determined whether this isan early stage shorting or a well-developed shorting (as indicated inFIG. 9(d)).

FIG. 10 shows the same WOLED panel shown in FIG. 9 after ashort-acceleration process. The dimensions given for the fuses on eachquarter of the panel correspond to the values listed in Table 1. Inparticular: quarter 1020 has fuses with length-to-width dimensions 15μm×20 μm, and a melting current of 10 mA; quarter 1030 has fuses withlength-to-width dimensions 15 μm×30 μm and a melting current of 15 mA;quarter 1040 has fuses with length-to-width dimensions 15 um×40 um and amelting current of 20 mA; and finally quarter 1050 has fuses withlength-to-width 20 μm×25 μm and a melting current of 15 mA. The meltingcurrent indicated for the fuses of each quarter is the current at whichthe fuse is designed to open an electrical connection. The dark spotslabeled with numbers 1001 through 1015 are spots where shorts occurredin the device and where the fuse opened to electrically isolate theshorted pixel. The microscopic images of shorting pixels marked in FIG.10 are shown in FIG. 11, where each of the shorts labeled 1001-1015correspond to one another. That is, shorts 1001-1006 are from panel1020; shorts 1007-1009 are from panel 1030; short 1010 is from panel1040; and shorts 1011-1015 are from panel 1050.

FIGS. 12(a)-(d) shows an exemplary embodiment wherein an integrated busline is utilized. More specifically, FIG. 12(a) shows the embodiment ofthe first device in normal operation; FIG. 12(b) shows a cross-sectionalview of this exemplary embodiment in normal operation; FIG. 12(c) showsthe same embodiment of the first device after a fault has occurred; andfinally FIG. 12(d) shows a cross-sectional view of this exemplaryembodiment after a fault has occurred.

In this exemplary embodiment, the cathode is divided into small islands,wherein the small islands comprise the first electrodes 1201 of aplurality of OLED circuit elements. The first electrode 1201 of each ofthe OLED circuit elements may also be the fuse. An interconnected busline layer 1202 may be disposed over and/or between the first electrodes1201 of the OLED circuit elements, as shown in FIG. 12(a).

More specifically, in this exemplary embodiment of the first device, thesecond electrode 1204 is shown as being disposed over the substrate1203, the organic EL material 1205 is disposed over the second electrode1204, the first electrode 1201 is patterned and is disposed over theorganic EL material 1205, and the first device further includes anintegrated bus line 1202. The integrated bus line 1202 electricallyconnects the first electrode 1201 of each of the OLED circuit elementstogether. The first electrode 1201 of each of the plurality of OLEDcircuit elements may also comprise a fuse. Preferably, in someembodiments, the first electrode 1201 is ablated in response to a shortcircuit (i.e. the excess current that results from the short circuit).This is shown in FIGS. 12(c) and (d) where the first electrode 1206 isshown as having been ablated, thereby opening the electrical circuit. Insome embodiments, the integrated bus line 1202 may be disposed overand/or between the plurality of OLED circuit elements (or a portionthereof, as shown in FIG. 12(b)).

According to some embodiments, when a short is developed in the firstelectrode 1201 of one of the OLED circuit elements (e.g. the electrode1206 shown as the 4^(th) row, 3^(rd) column in FIG. 12(c)), the excesscurrent will ablate the thin cathode island 1206 and stop the currentflow through this pixel. Some of the potential advantages of thisexemplary embodiment may include (1) high sensitivity; and (2) becausethe first electrodes 1201 are isolated from each of the other firstelectrodes, a short will only cause ablation in one thin cathode island(e.g. the first electrode 1206 shown in FIGS. 12(c) and (d)), and maynot affect neighboring islands. The sensitivity (“S”) of this embodimentmay be calculated as follows:I _(on) =I ₀/(n _(row) *n _(column))I _(off) =I ₀.S=I _(off) /I _(on) =n _(row) *n _(column)

Fuses as disclosed herein may be used to serve two purposes. First,fuses may provide electrical protection for individual pixels aspreviously described. Alternatively or in addition, fuses may provide ameans to allow for areas of the panel to be made non-emitting, such asfor signage applications. Thus, one potential application of devicesincorporating fuses as disclosed herein may be to develop signs ofarbitrary shape that can be programmed for a specific image after apanel has been manufactured. Thus, as disclosed herein, customized signsmay be produced based upon a common, standard OLED lighting paneldesign. Such techniques may be cheaper and preferable to using a custommask set for each design to be produced.

In some embodiments, specific fuses may be intentionally ablated asdisclosed herein, or otherwise opened so as to produce a pre-definedpattern of pixels and thus form a pre-determined image on an OLED panel.Referring, for example, to FIG. 8, it is apparent that the area of afuse typically is much less than the area of the associated pixel. Forexample, the typical area for a fuse may be about 20 μm×20 μm, comparedto about 1 mm×1 mm for a pixel. Thus, the area to be ablated for eachpixel is much less than the area of the pixel itself, which results inreduced processing time and contamination of a panel.

Generally, fuses may be ablated or otherwise opened efficiently byapplying energy to the fuse, causing it to open as previously described.For example, individual fuses may be ablated using various types oflaser to ablate the ITO layer of the fuse as previously described.Generally, any laser that is transparent through glass, plastic, orother similar layers in an OLED, while being absorbed by the ITO, may beused. Examples of such lasers include UV and IR (about 1 μm) lasers.Neodymium- or ytterbium-doped YAG lasers typically operate in the 1-μmregion. At this wavelength, ITO can be very absorptive, while typicalsubstrate materials such as glass and plastic are very transparent. Inaddition, typical thin film barrier coatings are also very transparentat this wavelength. As a result, ITO can be easily ablated by an IRlaser without damaging the device.

FIGS. 22 and 23 show example OLED panels fabricated according to atechnique in which some fuses have been opened by applying energy to thefuse. FIG. 22 shows an example of a pixelated panel in which most of thefuses in the panel have been ablated or otherwise opened. In theexample, 10 active pixels remain (i.e., have not had the associatedfuses opened) to form the letter “T”. FIG. 23 shows an example panel inwhich a portion of fuses have been opened to provide a sign showing theInternational Symbol of Access. As will be understood by one of skill inthe art, depending upon the configuration desired, a sign such as shownin FIG. 23 may be fabricated by opening fuses associated with the shaded(black) pixels in FIG. 23, or by opening fuses associated with theunshaded (white) pixels.

In some embodiments, the fuses that are opened by applying energy maycorrespond to pixels of a particular color. For example, the sign shownin FIG. 23 may be fabricated such that the background unshaded pixelsare blue, and the shaded pixels of the image are white, to achieve thestandard coloring for the Symbol. In this example, an initialwhite-emitting panel may be used, and fuses associated with non-bluepixels may be opened in each background area. More generally, in someembodiments fuses associated with pixels that emit a particular colormay be opened, allowing for a static panel that includes regions thatemit light of any desired color. Such a panel may be “static” because,in contrast to a programmable or color-tunable panel, the color emittedby any given region of the panel will be the same when the panel isactivated. Such a panel may be more efficient and/or require lesscontrolling circuitry than a conventional programmable panel. Somemulti- or full-color panels may include stripes of pixels, where eachstripe is configured to emit light of a specific color, such as red,green, or blue, for example as described in U.S. Pat. Nos. 7,663,300 and8,100,734, the disclosure of each of which is incorporated by referencein its entirety. In some embodiments, a region of a panel may beconfigured to emit a desired color by ablating or otherwise openingfuses associated with pixels in specific stripes or portions of stripesin the region. For example, if a region of a panel is desired to emitred light, fuses for the green and blue stripes in that region may beopened. Other desired colors may be achieved by opening fuses forportions of different stripes in a region, as will be readily understoodby one of skill in the art.

One technique of opening a fuse may be to apply energy, such as a laser,to ablate all or a portion of the fuse. More generally, an OLED may berendered non-emissive by applying energy to a component of an OLED, suchas a fuse associated with the OLED, to cause the component of the OLEDto be essentially non-conductive. As used herein, a component isessentially non-conductive if it is not more than about 1/1000^(th) asconductive as before application of energy to the component. Thus, forexample, when a fuse is opened as disclosed herein, it may be1/1000^(th) as conductive as before it was opened.

As previously described herein, each fuse in a panel typically mayoccupy a much smaller area than the associated pixel, i.e., the pixel towhich the fuse limits current flow. In some embodiments, the area ofeach fuse may be not more than 10%, 7%, 5% or 1% of the area of theassociated pixel to which the fuse limits current. In addition, thetotal area of components, such as fuses, to which energy is applied torender the components essentially non-conductive, may be a relativelysmall portion of the overall area of the associated OLEDs. For example,where fuses in a particular region of an OLED panel are caused to beessentially non-conductive, the area encompassed by the fuses may be notmore than 10% of the total area of the OLEDs in the region of the panel.

As is known in the art, OLEDs and OLED devices may be encapsulated, forexample to prevent damage to the OLED components. As disclosed herein,one or more fuses in an OLED panel may be opened prior to, or subsequentto, such encapsulation. That is, in some embodiments the energy used toopen a fuse may be applied through such an encapsulation, or may beapplied prior to application of an encapsulation layer.

Some embodiments also include devices made as disclosed herein, i.e., byapplying energy to one or more components in an OLED panel to cause thecomponents to become essentially non-conductive. Such a device mayinclude multiple pixels connected to a bus line through a fuse. Lightemitted by such a device may have a total active area less than thepanel as initially constructed, due to the portion of the device thathas been rendered partially or entirely non-emissive as disclosedherein.

Experimental Fabrication and Results

Exemplary fuses with different geometric designs were investigated, andthe relationship between geometric dimension and melting current wasfurther studied by the inventors. For these exemplary devices, testinglayouts were designed and 800 Å ITO was patterned into two 1 mm×1 mmcontact pads 1302 with one or multiple narrow bridges in between whichwill function as the fuse 1301. FIGS. 13(a) and (b) show the layouts ofthe testing pattern with one L×W=15 μm×30 μm fuse 1301 and three L×W=15μm×10 μm fuses 1301, where L is the length along the current flowdirection and W is the width perpendicular to the current flowdirection. Table 2 below lists all the designs utilized in thisexperiment with various L and W values used in this test. It should benoted that the numbers of L and W used in this example are the designeddimensions, whereas the fabricated fuse may have different dimensionsbased on the fabrication process.

TABLE 2 Dimensions of fuses in the testing panel L [μm] 10 15 20 25 2525 W [μm] 10 15 20 25 30 40

Current-voltage IV characteristics of the experimental fuses were testedusing an Agilent 4155C Semiconductor Parameter Analyzer, which iscommercially available. FIG. 14 shows an example of the IV curves of aset of fuses with the same length L=20 μm, and various widths W from 10μm to 40 μm. The voltage was applied to the contact pads 1302 and sweptfrom 0 V to 8 V. The resistances of the fuses were extracted from a lowvoltage sweep from approximately −0.05 V to 0.05 V, as listed in thegraph next to the width values (e.g. fuse 1401 has width=10 μm andresistance=184Ω; fuse 1402 has width=15 μm and resistance=163Ω; fuse1403 has width=20 μm and resistance=131Ω; fuse 1404 has width=25 μm andresistance=119Ω; fuse 1405 has width=30 μm and resistance=118Ω; and fuse1406 has width=40 μm and resistance=110Ω).

As shown in FIG. 14, the fuses function similar to a resistor in thebeginning (i.e. at low voltages) and the current rises almost linearlydependent on the voltage. At a certain voltage, the current reaches apeak value and then drops, followed by a much gentler (i.e. gradual) IVslope, which implies an increasing of the fuse resistance. Withcontinued reference to FIG. 14, after a short period of continuousbiasing, the current drops to zero, indicating that the fuse is fullyopen and has created an open circuit. As defined above, the maximum fusecurrent is the “melting current” I_(M).

As shown in FIG. 14, it was also found that with an increase of fusewidth, the melting current I_(M) is also increased (i.e., the meltingcurrent for fuse 1406 is greater than for fuse 1405, which is greaterthan for fuse 1404, etc.). This is may be due in part to fact that thenormal resistance of the fuse at room temperature (R) is inverselyproportional to the width W. Therefore the wider the fuse (i.e. thelarger W is), the lower the resistance, and the higher the current thatmay be required to generate enough Joule heat (I²R) to burn, melt,ablate, crack or otherwise physically or chemically alter the materialand open up the fuse.

The inventors have also found that the breaking down of an ITO fuse maycomprises two or more stages, as indicated in FIG. 15: one or morephysical cracks may be formed in Stage 1, and the fuse material may beburned in Stage 2, the combination of which causes the ultimate openingof the fuse. A potential explanation for these states is as follows: inStage 1, normal current I flows through the fuse having a resistance R(initially functioning as a resistor) and generates Joule heating (equalto I²R), which heats up the material of the fuse. One or more cracks maythen develop because of the compressive strain caused by the mismatchedthermal expansion coefficient (CTE) of thin film ITO (10.2×10⁻⁶/° C.)(see, e.g. D. G. Neerinck and T. J. Vink, Depth Profiling of Thin ITOFilms By Grazing Incidence X-ray Diffraction, Thin Solid Films, 278, 12(1996), which is hereby incorporated by reference in its entirety) andglass substrate (37.8×10⁻⁷/° C.) (see, e.g., D. Bhattacharyya and M. J.Carter, Effect of Substrate On The Structural and Optical Properties ofChemical-Bath-Deposited CdS Films, Thin Solid Films, 288, 176 (1996),which is hereby incorporated by reference in its entirety). Even withone or more cracks, the thin film may not be completely discontinuous,but the resistance of the fuse may rise dramatically, and hence generatemore heat when current flows through the fuse so as to burn the materialin Stage 2. This is correspondent to the IV curve of a typical ITO fuseshown in FIG. 16, where during Stage 1, the current reaches the peakvalue just before the cracking of the fuse occurs, and then the currentfalls into Stage 2 (i.e. at a lower level of current) for a short periodof time until the fuse is open (i.e. at the melting current of the fuse1601).

The inventors also studied multiple-fuse structures. Generally, underthe same bias condition, a resistor with a width W has the sameresistance as n resistors connected in parallel each having a width ofW/n. For example, a single fuse with L×W=15 μm×30 μm in FIG. 13(a) iselectrically equivalent to the three fuses with L×W=15 μm×10 μm in FIG.13(b), as far as its resistance. However, due to process limitations(i.e. real world conditions that may result in fabrication errors orimperfections), the ITO layer may typically be over-etched, which mayresult in fuses with longer L and narrower W than those that aredesigned. The difference between the designed value and the real valuemay be defined as ΔL and ΔW. Table 3 below compares ΔW caused by theprocess limitation for various widths found by the inventors during theexperiments.

TABLE 3 Comparison of ΔW at various width values Designed W [μm] 10 1520 25 30 40 Measured W [μm] 8 13 15 20 24 33 ΔW [μm] 2 2 5 5 6 7

IV curves of single fuses vs. multiple fuses plotted in FIG. 17, wherethe IV slopes (representing the resistance values) of multiple fuses(i.e. graphs 1704, 1705, and 1706) are steeper than those of singlefuses (i.e. graphs 1701, 1702, and 1703). The multiple fuses also burnat a higher current than equivalent single fuses. That is, for instance,fuses 1704 (comprising two designed 10×10 μm fuses) burns at a highercurrent than fuse 1701 (comprising a single designed 10×20 μm fuse);fuses 1705 (comprising three designed 10×10 μm fuses) burns at a highercurrent than the fuse 1702 (comprising a single designed 10×30 μm fuse);and fuses 1706 (comprising four designed 10×10 μm fuses) burns at ahigher current than the fuse 1703 (comprising a single designed 10×40 μmfuse). One possible explanation of this is that heat may be dissipatedmore readily in multiple smaller fuses than in a single larger fuse.Using multiple fuses may be advantageous in some applications when it isdesired that the fuse be capable of sustaining a high current surgewithout opening the electrical circuit. In addition, the inventors alsofound that the burning procedure of multiple fuses is smoother than thatof a single fuse, where usually abrupt current rise occurs during thevoltage sweep. This can also be seen in FIG. 17.

The inventors have also experimented by using different types of metalfor various fuse applications. FIG. 18 shows the IV curves of 10nm-thick aluminum (Al) fuses, with various geometric designs. Similar tothe ITO fuses, generally the wider the Al fuse, the lower the resistanceand the higher the melting current. However, the inventors found thatthe Al fuses show a very sharp instant breakdown, instead of a two-stageprocess as observed with ITO fuses. A clear break was found in the openfuse, as can be seen in FIG. 19. This may be due, in part, to the thinfilm Al having a higher coefficient of thermal expansion (CTE) (e.g.greater than 15×10⁻⁶/° C.) than ITO (see, e.g. W. Fang and C.-Y. Lo,Sensors and Actuators, 84, 310-314 (2000), which is hereby incorporatedby reference in its entirety). Therefore, the Al fuses may be easier tobreak on a glass substrate. In addition, Al has a lower melting point(approximately 933 K) than that of ITO (approximately 1800-2200 K), andthe melting point further reduces when the film thickness is decreased.

The inventor also experimented with Al fuses with different thicknesses,as shown in FIG. 20. The IV comparison of the same L×W=0.3 mm×0.4 mmfuses made from 10 nm (plot 2002) and 20 nm (plot 2001) Al were plottedin FIG. 20. With a film thickness twice as large, the resistance of the20 nm-thick fuse 2001 was approximately half of the resistance of the 10nm-thick fuse 2002, resulting in a higher melting current.

The general design rules developed by the inventors for incorporatingfuses in a lighting panel are described below for exemplary purposesonly. First, the working condition of the lighting panel may need to bedetermined, which usually refers to the desired luminance levels. Basedon the current density-voltage-luminance (JVL) relationship, the drivingcondition at designated luminance levels may be determined. If the panelis designed to be dimmable, which means the panel may work at variousluminance levels (e.g. from 500 cd/m² to 5000 cd/m²), the workingcondition may also vary according to the luminance. In this exemplarycase, minimum (I_(min)) and maximum (I_(max)) total panel current may bedetermined based on the lowest and highest luminance levels (assuming aconstant-current driving configuration). For example, assuming the panelhas n pixels that have the same (or approximately the same) emissiveareas and device structures, the total panel current may beapproximately equally divided, and each pixel will then have the minimumand maximum pixel current of approximately I_(min)/n and I_(max)/n. Therated current I_(N) (i.e. the maximum current that a fuse cancontinuously conduct without interrupting the circuit), may be equal toapproximately I_(max)/n.

In general, the melting current (IM) of the fuse should be greater thanthe maximum pixel current (e.g. I_(max)/n), yet lower than the minimumpanel current (e.g. I_(min)). The fuses may be designed to open eitherat a low or high current level depending on the specification of thepanel and/or the application it is intended to be used for. For example,I_(M) (the melting current) may be set at a relatively low point closerto I_(max)/n, so that any excess current greater than the rated currentwill open up the fuse. In such circumstances, if a short develops (orbegins to develop) in a pixel, the fuse may burn very quickly andisolate the shorting pixel from the normally operating ones, which mayprevent the accumulation of local heating and safely protect the rest ofthe panel. This approach may favor an initial panel screening process,where any potential shorting is preferred to be detected and eliminatedas fast as possible. On the other hand, in some embodiments, I_(M) maybe designed at a relatively high current level closer to I_(min), sothat the circuit can sustain some degree of excess current surge withoutshutting off any normally operating pixels.

In general, there may be various ways to choose the melting current INrbased on a customized specification. In practice, instead of settingI_(M) right at I_(max)/n or I_(min), the melting current may typicallybe set somewhere above I_(max)/n and/or somewhere below I_(min) so as toleave some tolerance (e.g. this will permit some initial increase incurrent or fluctuation). For example, with the opening of fuses (e.g.during operation of embodiments that may comprise fuses connected inseries with each pixel), the total pixel number n decreases dynamically,which results in the increasing of the current supplied to each pixelbased on I_(max)/n. Therefore, more tolerance may be needed above thecurrent I_(max)/n, to avoid electrically isolating normally operatingpixels when the total number of pixels goes down. In some embodiments,I_(M) may be designed as β(I_(max)/n), where β is greater than 1. Insome embodiments, I_(M) may be designed as ε(I_(min)), where ε is lessthan 1. In some embodiments, I_(M) may be designed to fall within arange of [β(I_(max)/n), ε(I_(min))]. FIG. 21 provides a graphicalillustration of the relationship of the currents described above, wherethe region 2101 refers to the values of the melting current of the fusesthat may be selected such that the device may function properly, and theshadow region 2102 represents the designated I_(M) for a particularembodiment. For instance, a melting current may be set at two timesgreater than the maximum pixel current, i.e., β=2, andI_(M)≧2·(I_(max)/n). If the maximum panel current I_(max)=200 mA, andthe total number of pixels n=20000, then the melting currentI_(M)≧2×(200/20000 mA)=20 mA.

Once the range of melting current has been determined, the resistancerange of the fuse may be accordingly determined, and the additionalresistive power loss may then be evaluated. Given the working condition,the current density J of the panel can be determined as well as thecurrent going through each pixel I_(pixel)=J·A, where A is the emissivearea of each pixel (assuming all pixels are of the same size). Thepotential drop due to the fuse resistor is given by ΔV=J·A·R, and thepower loss is ΔP=(J·A)²·R. According to the exemplary designspecifications, R may be further refined to a desired value to meet therequirement of ΔV and/or ΔP. Continuing with the above example, wherethe maximum pixel current I_(pixel)=200/20000 mA=0.01 mA. With referenceto FIG. 14, an 800 Å ITO fuse 1403 with L×W=20 μm×20 μm, and resistanceR=131Ω, can open at approximately I_(M)=22.5 mA, which is within therange of the desired melting current. In this exemplary case, thepotential drop across the fuse ΔV=0.01 mA×131Ω≈0.00131 V, and the powerloss due to the fuse resistor is approximatelyΔP=(0.01×10⁻³)²×131Ω=1.31×10⁻⁵ mW. This also illustrates that the use offuses does not necessarily introduce much power loss, which may belargely due to the low current level going through each fuse toward thepixel during normal operation.

After the melting current and resistance are determined for the fuse,the geometric shape and the material of the fuse can be decidedaccording to the experimental results, in association with the processcapability.

In combination with the use of fuses, an additional protecting circuitmay be designed to provide feedback on current and/or voltage of thepanel so as to control the speed of opening fuses. For example, underconstant-current driving configuration, when a short occurs, the voltagewill drop accordingly. The protecting circuit may be designed to detectthe decrease of voltage and return a higher current pulse so that thefuse connecting to the problematic pixel can open quickly withoutaccumulating too much heat, thereby protecting the OLED from anyresulting damage/degradation, particularly the EL material.

It is understood that the various embodiments described herein are byway of example only, and are not intended to limit the scope of theinvention. For example, many of the materials and structures describedherein may be substituted with other materials and structures withoutdeviating from the spirit of the invention. The present invention asclaimed may therefore include variations from the particular examplesand preferred embodiments described herein, as will be apparent to oneof skill in the art. It is understood that various theories as to whythe invention works are not intended to be limiting.

The above description is illustrative and is not restrictive. Manyvariations of the invention will become apparent to those skilled in theart upon review of the disclosure. The scope of the invention should,therefore, be determined not with reference to the above description,but instead should be determined with reference to the pending claimsalong with their full scope or equivalents.

Although many embodiments were described above as comprising differentfeatures and/or combination of features, a person of ordinary skill inthe art after reading this disclosure may understand that in someinstances, one or more of these components could be combined with any ofthe components or features described above. That is, one or morefeatures from any embodiment can be combined with one or more featuresof any other embodiment without departing from the scope of theinvention.

As noted previously, all measurements, dimensions, and materialsprovided herein within the specification or within the figures are byway of example only.

A recitation of “a,” “an,” or “the” is intended to mean “one or more”unless specifically indicated to the contrary.

All publications mentioned herein are incorporated herein by referenceto disclose and describe the methods and/or materials in connection withwhich the publications are cited. The publications discussed herein areprovided solely for their disclosure prior to the filing date of thepresent application. Nothing herein is to be construed as an admissionthat the present invention is not entitled to antedate such publicationby virtue of prior invention. Further, the dates of publication providedmay be different from the actual publication dates, which may need to beindependently confirmed.

What is claimed is:
 1. A method comprising: obtaining a substrate havinga first electrode; depositing organic emissive material over the firstelectrode; depositing a plurality of physically segmented secondelectrodes over the organic emissive material; depositing insulatingmaterial over the physically segmented second electrodes, wherein aportion of each of the second electrodes remains exposed through theinsulating material; depositing an unpatterned blanket layer of aconductive material such that the blanket layer of conductive materialelectrically connects to the portion of each of the second electrodesthat remains exposed through the insulating material, to form aplurality of pixels, each pixel being electrically connected to a fusethat limits current to the pixel; selecting a plurality of fuses in theOLED panel; and applying energy to each fuse of the selected pluralityof fuses to cause the fuse to be opened.
 2. The method of claim 1,wherein each fuse of the selected plurality of fuses occupies an area ofthe panel that is not more than 10% of the area of the panel occupied bythe pixel to which the fuse limits current.
 3. The method of claim 1,wherein the step of applying energy to the selected plurality of fusescomprises directing a laser at each of the plurality of fuses to ablateeach of the selected group of fuses.
 4. The method of claim 3, whereinthe laser is a type selected from the group consisting of: anultraviolet (UV) laser, and an infrared (IR) laser.
 5. The method ofclaim 1, wherein the area of each of the plurality of fuses is not morethan about 400 μm².
 6. The method of claim 1, wherein the OLED panelcomprises at least one material type selected from the group consistingof: a transparent material, a flexible material, and a plastic.
 7. Themethod of claim 1, wherein the OLED panel is color-tunable.
 8. Themethod of claim 7, wherein the OLED panel comprises a plurality ofstripes, each stripe configured to emit red, green, or blue light. 9.The method of claim 8, wherein the plurality of selected fuses includesa first group of fuses that limits current to pixels in a stripe of afirst color in a first region of the panel.
 10. The method of claim 9,wherein the plurality of selected fuses includes a second group of fusesthat limits current to pixels in a stripe of a second color in a secondregion of the panel.
 11. The method of claim 9, wherein the plurality ofselected fuses includes a second group of fuses that limits current topixels in a stripe of a second color in the first region of the panel.12. A device fabricated according to the method of claim
 1. 13. A methodcomprising: obtaining a substrate having a patterned first electrode,the patterned first electrode comprising a plurality of electroderegions; depositing organic emissive material over the patterned firstelectrode; depositing a second electrode over the organic emissivematerial; disposing a bus line over the substrate; wherein each of theplurality of electrode regions is electrically connected to one of theplurality of pixels, and connected to the bus line through one of theplurality of fuses in the OLED panel; selecting a plurality of fuses inthe OLED panel; and applying energy to each fuse of the selectedplurality of fuses to cause the fuse to be opened.
 14. The method ofclaim 13, wherein each fuse of the selected plurality of fuses occupiesan area of the panel that is not more than 10% of the area of the paneloccupied by the pixel to which the fuse limits current.
 15. The methodof claim 13, wherein the step of applying energy to the selectedplurality of fuses comprises directing a laser at each of the pluralityof fuses to ablate each of the selected group of fuses.
 16. The methodof claim 15, wherein the laser is a type selected from the groupconsisting of: an ultraviolet (UV) laser, and an infrared (IR) laser.17. The method of claim 13, wherein the area of each of the plurality offuses is not more than about 400 μm².
 18. The method of claim 13,wherein the OLED panel comprises at least one material type selectedfrom the group consisting of: a transparent material, a flexiblematerial, and a plastic.
 19. The method of claim 13, wherein the OLEDpanel is color-tunable.
 20. The method of claim 19, wherein the OLEDpanel comprises a plurality of stripes, each stripe configured to emitred, green, or blue light.
 21. The method of claim 20, wherein theplurality of selected fuses includes a first group of fuses that limitscurrent to pixels in a stripe of a first color in a first region of thepanel.
 22. The method of claim 21, wherein the plurality of selectedfuses includes a second group of fuses that limits current to pixels ina stripe of a second color in a second region of the panel.
 23. Themethod of claim 21, wherein the plurality of selected fuses includes asecond group of fuses that limits current to pixels in a stripe of asecond color in the first region of the panel.
 24. A device fabricatedaccording to the method of claim 13.